Adding upstream version 6.1.76.upstream/6.1.76upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1547 insertions, 0 deletions

diff --git a/drivers/usb/musb/cppi_dma.c b/drivers/usb/musb/cppi_dma.c
new file mode 100644
index 000000000..edb5b63d7
--- /dev/null
+++ b/drivers/usb/musb/cppi_dma.c
@@ -0,0 +1,1547 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2005-2006 by Texas Instruments
+ *
+ * This file implements a DMA  interface using TI's CPPI DMA.
+ * For now it's DaVinci-only, but CPPI isn't specific to DaVinci or USB.
+ * The TUSB6020, using VLYNQ, has CPPI that looks much like DaVinci.
+ */
+
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+#include <linux/usb.h>
+
+#include "musb_core.h"
+#include "musb_debug.h"
+#include "cppi_dma.h"
+#include "davinci.h"
+
+
+/* CPPI DMA status 7-mar-2006:
+ *
+ * - See musb_{host,gadget}.c for more info
+ *
+ * - Correct RX DMA generally forces the engine into irq-per-packet mode,
+ *   which can easily saturate the CPU under non-mass-storage loads.
+ *
+ * NOTES 24-aug-2006 (2.6.18-rc4):
+ *
+ * - peripheral RXDMA wedged in a test with packets of length 512/512/1.
+ *   evidently after the 1 byte packet was received and acked, the queue
+ *   of BDs got garbaged so it wouldn't empty the fifo.  (rxcsr 0x2003,
+ *   and RX DMA0: 4 left, 80000000 8feff880, 8feff860 8feff860; 8f321401
+ *   004001ff 00000001 .. 8feff860)  Host was just getting NAKed on tx
+ *   of its next (512 byte) packet.  IRQ issues?
+ *
+ * REVISIT:  the "transfer DMA" glue between CPPI and USB fifos will
+ * evidently also directly update the RX and TX CSRs ... so audit all
+ * host and peripheral side DMA code to avoid CSR access after DMA has
+ * been started.
+ */
+
+/* REVISIT now we can avoid preallocating these descriptors; or
+ * more simply, switch to a global freelist not per-channel ones.
+ * Note: at full speed, 64 descriptors == 4K bulk data.
+ */
+#define NUM_TXCHAN_BD       64
+#define NUM_RXCHAN_BD       64
+
+static inline void cpu_drain_writebuffer(void)
+{
+	wmb();
+#ifdef	CONFIG_CPU_ARM926T
+	/* REVISIT this "should not be needed",
+	 * but lack of it sure seemed to hurt ...
+	 */
+	asm("mcr p15, 0, r0, c7, c10, 4 @ drain write buffer\n");
+#endif
+}
+
+static inline struct cppi_descriptor *cppi_bd_alloc(struct cppi_channel *c)
+{
+	struct cppi_descriptor	*bd = c->freelist;
+
+	if (bd)
+		c->freelist = bd->next;
+	return bd;
+}
+
+static inline void
+cppi_bd_free(struct cppi_channel *c, struct cppi_descriptor *bd)
+{
+	if (!bd)
+		return;
+	bd->next = c->freelist;
+	c->freelist = bd;
+}
+
+/*
+ *  Start DMA controller
+ *
+ *  Initialize the DMA controller as necessary.
+ */
+
+/* zero out entire rx state RAM entry for the channel */
+static void cppi_reset_rx(struct cppi_rx_stateram __iomem *rx)
+{
+	musb_writel(&rx->rx_skipbytes, 0, 0);
+	musb_writel(&rx->rx_head, 0, 0);
+	musb_writel(&rx->rx_sop, 0, 0);
+	musb_writel(&rx->rx_current, 0, 0);
+	musb_writel(&rx->rx_buf_current, 0, 0);
+	musb_writel(&rx->rx_len_len, 0, 0);
+	musb_writel(&rx->rx_cnt_cnt, 0, 0);
+}
+
+/* zero out entire tx state RAM entry for the channel */
+static void cppi_reset_tx(struct cppi_tx_stateram __iomem *tx, u32 ptr)
+{
+	musb_writel(&tx->tx_head, 0, 0);
+	musb_writel(&tx->tx_buf, 0, 0);
+	musb_writel(&tx->tx_current, 0, 0);
+	musb_writel(&tx->tx_buf_current, 0, 0);
+	musb_writel(&tx->tx_info, 0, 0);
+	musb_writel(&tx->tx_rem_len, 0, 0);
+	/* musb_writel(&tx->tx_dummy, 0, 0); */
+	musb_writel(&tx->tx_complete, 0, ptr);
+}
+
+static void cppi_pool_init(struct cppi *cppi, struct cppi_channel *c)
+{
+	int	j;
+
+	/* initialize channel fields */
+	c->head = NULL;
+	c->tail = NULL;
+	c->last_processed = NULL;
+	c->channel.status = MUSB_DMA_STATUS_UNKNOWN;
+	c->controller = cppi;
+	c->is_rndis = 0;
+	c->freelist = NULL;
+
+	/* build the BD Free list for the channel */
+	for (j = 0; j < NUM_TXCHAN_BD + 1; j++) {
+		struct cppi_descriptor	*bd;
+		dma_addr_t		dma;
+
+		bd = dma_pool_alloc(cppi->pool, GFP_KERNEL, &dma);
+		bd->dma = dma;
+		cppi_bd_free(c, bd);
+	}
+}
+
+static int cppi_channel_abort(struct dma_channel *);
+
+static void cppi_pool_free(struct cppi_channel *c)
+{
+	struct cppi		*cppi = c->controller;
+	struct cppi_descriptor	*bd;
+
+	(void) cppi_channel_abort(&c->channel);
+	c->channel.status = MUSB_DMA_STATUS_UNKNOWN;
+	c->controller = NULL;
+
+	/* free all its bds */
+	bd = c->last_processed;
+	do {
+		if (bd)
+			dma_pool_free(cppi->pool, bd, bd->dma);
+		bd = cppi_bd_alloc(c);
+	} while (bd);
+	c->last_processed = NULL;
+}
+
+static void cppi_controller_start(struct cppi *controller)
+{
+	void __iomem	*tibase;
+	int		i;
+
+	/* do whatever is necessary to start controller */
+	for (i = 0; i < ARRAY_SIZE(controller->tx); i++) {
+		controller->tx[i].transmit = true;
+		controller->tx[i].index = i;
+	}
+	for (i = 0; i < ARRAY_SIZE(controller->rx); i++) {
+		controller->rx[i].transmit = false;
+		controller->rx[i].index = i;
+	}
+
+	/* setup BD list on a per channel basis */
+	for (i = 0; i < ARRAY_SIZE(controller->tx); i++)
+		cppi_pool_init(controller, controller->tx + i);
+	for (i = 0; i < ARRAY_SIZE(controller->rx); i++)
+		cppi_pool_init(controller, controller->rx + i);
+
+	tibase =  controller->tibase;
+	INIT_LIST_HEAD(&controller->tx_complete);
+
+	/* initialise tx/rx channel head pointers to zero */
+	for (i = 0; i < ARRAY_SIZE(controller->tx); i++) {
+		struct cppi_channel	*tx_ch = controller->tx + i;
+		struct cppi_tx_stateram __iomem *tx;
+
+		INIT_LIST_HEAD(&tx_ch->tx_complete);
+
+		tx = tibase + DAVINCI_TXCPPI_STATERAM_OFFSET(i);
+		tx_ch->state_ram = tx;
+		cppi_reset_tx(tx, 0);
+	}
+	for (i = 0; i < ARRAY_SIZE(controller->rx); i++) {
+		struct cppi_channel	*rx_ch = controller->rx + i;
+		struct cppi_rx_stateram __iomem *rx;
+
+		INIT_LIST_HEAD(&rx_ch->tx_complete);
+
+		rx = tibase + DAVINCI_RXCPPI_STATERAM_OFFSET(i);
+		rx_ch->state_ram = rx;
+		cppi_reset_rx(rx);
+	}
+
+	/* enable individual cppi channels */
+	musb_writel(tibase, DAVINCI_TXCPPI_INTENAB_REG,
+			DAVINCI_DMA_ALL_CHANNELS_ENABLE);
+	musb_writel(tibase, DAVINCI_RXCPPI_INTENAB_REG,
+			DAVINCI_DMA_ALL_CHANNELS_ENABLE);
+
+	/* enable tx/rx CPPI control */
+	musb_writel(tibase, DAVINCI_TXCPPI_CTRL_REG, DAVINCI_DMA_CTRL_ENABLE);
+	musb_writel(tibase, DAVINCI_RXCPPI_CTRL_REG, DAVINCI_DMA_CTRL_ENABLE);
+
+	/* disable RNDIS mode, also host rx RNDIS autorequest */
+	musb_writel(tibase, DAVINCI_RNDIS_REG, 0);
+	musb_writel(tibase, DAVINCI_AUTOREQ_REG, 0);
+}
+
+/*
+ *  Stop DMA controller
+ *
+ *  De-Init the DMA controller as necessary.
+ */
+
+static void cppi_controller_stop(struct cppi *controller)
+{
+	void __iomem		*tibase;
+	int			i;
+	struct musb		*musb;
+
+	musb = controller->controller.musb;
+
+	tibase = controller->tibase;
+	/* DISABLE INDIVIDUAL CHANNEL Interrupts */
+	musb_writel(tibase, DAVINCI_TXCPPI_INTCLR_REG,
+			DAVINCI_DMA_ALL_CHANNELS_ENABLE);
+	musb_writel(tibase, DAVINCI_RXCPPI_INTCLR_REG,
+			DAVINCI_DMA_ALL_CHANNELS_ENABLE);
+
+	musb_dbg(musb, "Tearing down RX and TX Channels");
+	for (i = 0; i < ARRAY_SIZE(controller->tx); i++) {
+		/* FIXME restructure of txdma to use bds like rxdma */
+		controller->tx[i].last_processed = NULL;
+		cppi_pool_free(controller->tx + i);
+	}
+	for (i = 0; i < ARRAY_SIZE(controller->rx); i++)
+		cppi_pool_free(controller->rx + i);
+
+	/* in Tx Case proper teardown is supported. We resort to disabling
+	 * Tx/Rx CPPI after cleanup of Tx channels. Before TX teardown is
+	 * complete TX CPPI cannot be disabled.
+	 */
+	/*disable tx/rx cppi */
+	musb_writel(tibase, DAVINCI_TXCPPI_CTRL_REG, DAVINCI_DMA_CTRL_DISABLE);
+	musb_writel(tibase, DAVINCI_RXCPPI_CTRL_REG, DAVINCI_DMA_CTRL_DISABLE);
+}
+
+/* While dma channel is allocated, we only want the core irqs active
+ * for fault reports, otherwise we'd get irqs that we don't care about.
+ * Except for TX irqs, where dma done != fifo empty and reusable ...
+ *
+ * NOTE: docs don't say either way, but irq masking **enables** irqs.
+ *
+ * REVISIT same issue applies to pure PIO usage too, and non-cppi dma...
+ */
+static inline void core_rxirq_disable(void __iomem *tibase, unsigned epnum)
+{
+	musb_writel(tibase, DAVINCI_USB_INT_MASK_CLR_REG, 1 << (epnum + 8));
+}
+
+static inline void core_rxirq_enable(void __iomem *tibase, unsigned epnum)
+{
+	musb_writel(tibase, DAVINCI_USB_INT_MASK_SET_REG, 1 << (epnum + 8));
+}
+
+
+/*
+ * Allocate a CPPI Channel for DMA.  With CPPI, channels are bound to
+ * each transfer direction of a non-control endpoint, so allocating
+ * (and deallocating) is mostly a way to notice bad housekeeping on
+ * the software side.  We assume the irqs are always active.
+ */
+static struct dma_channel *
+cppi_channel_allocate(struct dma_controller *c,
+		struct musb_hw_ep *ep, u8 transmit)
+{
+	struct cppi		*controller;
+	u8			index;
+	struct cppi_channel	*cppi_ch;
+	void __iomem		*tibase;
+	struct musb		*musb;
+
+	controller = container_of(c, struct cppi, controller);
+	tibase = controller->tibase;
+	musb = c->musb;
+
+	/* ep0 doesn't use DMA; remember cppi indices are 0..N-1 */
+	index = ep->epnum - 1;
+
+	/* return the corresponding CPPI Channel Handle, and
+	 * probably disable the non-CPPI irq until we need it.
+	 */
+	if (transmit) {
+		if (index >= ARRAY_SIZE(controller->tx)) {
+			musb_dbg(musb, "no %cX%d CPPI channel", 'T', index);
+			return NULL;
+		}
+		cppi_ch = controller->tx + index;
+	} else {
+		if (index >= ARRAY_SIZE(controller->rx)) {
+			musb_dbg(musb, "no %cX%d CPPI channel", 'R', index);
+			return NULL;
+		}
+		cppi_ch = controller->rx + index;
+		core_rxirq_disable(tibase, ep->epnum);
+	}
+
+	/* REVISIT make this an error later once the same driver code works
+	 * with the other DMA engine too
+	 */
+	if (cppi_ch->hw_ep)
+		musb_dbg(musb, "re-allocating DMA%d %cX channel %p",
+				index, transmit ? 'T' : 'R', cppi_ch);
+	cppi_ch->hw_ep = ep;
+	cppi_ch->channel.status = MUSB_DMA_STATUS_FREE;
+	cppi_ch->channel.max_len = 0x7fffffff;
+
+	musb_dbg(musb, "Allocate CPPI%d %cX", index, transmit ? 'T' : 'R');
+	return &cppi_ch->channel;
+}
+
+/* Release a CPPI Channel.  */
+static void cppi_channel_release(struct dma_channel *channel)
+{
+	struct cppi_channel	*c;
+	void __iomem		*tibase;
+
+	/* REVISIT:  for paranoia, check state and abort if needed... */
+
+	c = container_of(channel, struct cppi_channel, channel);
+	tibase = c->controller->tibase;
+	if (!c->hw_ep)
+		musb_dbg(c->controller->controller.musb,
+			"releasing idle DMA channel %p", c);
+	else if (!c->transmit)
+		core_rxirq_enable(tibase, c->index + 1);
+
+	/* for now, leave its cppi IRQ enabled (we won't trigger it) */
+	c->hw_ep = NULL;
+	channel->status = MUSB_DMA_STATUS_UNKNOWN;
+}
+
+/* Context: controller irqlocked */
+static void
+cppi_dump_rx(int level, struct cppi_channel *c, const char *tag)
+{
+	void __iomem			*base = c->controller->mregs;
+	struct cppi_rx_stateram __iomem	*rx = c->state_ram;
+
+	musb_ep_select(base, c->index + 1);
+
+	musb_dbg(c->controller->controller.musb,
+		"RX DMA%d%s: %d left, csr %04x, "
+		"%08x H%08x S%08x C%08x, "
+		"B%08x L%08x %08x .. %08x",
+		c->index, tag,
+		musb_readl(c->controller->tibase,
+			DAVINCI_RXCPPI_BUFCNT0_REG + 4 * c->index),
+		musb_readw(c->hw_ep->regs, MUSB_RXCSR),
+
+		musb_readl(&rx->rx_skipbytes, 0),
+		musb_readl(&rx->rx_head, 0),
+		musb_readl(&rx->rx_sop, 0),
+		musb_readl(&rx->rx_current, 0),
+
+		musb_readl(&rx->rx_buf_current, 0),
+		musb_readl(&rx->rx_len_len, 0),
+		musb_readl(&rx->rx_cnt_cnt, 0),
+		musb_readl(&rx->rx_complete, 0)
+		);
+}
+
+/* Context: controller irqlocked */
+static void
+cppi_dump_tx(int level, struct cppi_channel *c, const char *tag)
+{
+	void __iomem			*base = c->controller->mregs;
+	struct cppi_tx_stateram __iomem	*tx = c->state_ram;
+
+	musb_ep_select(base, c->index + 1);
+
+	musb_dbg(c->controller->controller.musb,
+		"TX DMA%d%s: csr %04x, "
+		"H%08x S%08x C%08x %08x, "
+		"F%08x L%08x .. %08x",
+		c->index, tag,
+		musb_readw(c->hw_ep->regs, MUSB_TXCSR),
+
+		musb_readl(&tx->tx_head, 0),
+		musb_readl(&tx->tx_buf, 0),
+		musb_readl(&tx->tx_current, 0),
+		musb_readl(&tx->tx_buf_current, 0),
+
+		musb_readl(&tx->tx_info, 0),
+		musb_readl(&tx->tx_rem_len, 0),
+		/* dummy/unused word 6 */
+		musb_readl(&tx->tx_complete, 0)
+		);
+}
+
+/* Context: controller irqlocked */
+static inline void
+cppi_rndis_update(struct cppi_channel *c, int is_rx,
+		void __iomem *tibase, int is_rndis)
+{
+	/* we may need to change the rndis flag for this cppi channel */
+	if (c->is_rndis != is_rndis) {
+		u32	value = musb_readl(tibase, DAVINCI_RNDIS_REG);
+		u32	temp = 1 << (c->index);
+
+		if (is_rx)
+			temp <<= 16;
+		if (is_rndis)
+			value |= temp;
+		else
+			value &= ~temp;
+		musb_writel(tibase, DAVINCI_RNDIS_REG, value);
+		c->is_rndis = is_rndis;
+	}
+}
+
+static void cppi_dump_rxbd(const char *tag, struct cppi_descriptor *bd)
+{
+	pr_debug("RXBD/%s %08x: "
+			"nxt %08x buf %08x off.blen %08x opt.plen %08x\n",
+			tag, bd->dma,
+			bd->hw_next, bd->hw_bufp, bd->hw_off_len,
+			bd->hw_options);
+}
+
+static void cppi_dump_rxq(int level, const char *tag, struct cppi_channel *rx)
+{
+	struct cppi_descriptor	*bd;
+
+	cppi_dump_rx(level, rx, tag);
+	if (rx->last_processed)
+		cppi_dump_rxbd("last", rx->last_processed);
+	for (bd = rx->head; bd; bd = bd->next)
+		cppi_dump_rxbd("active", bd);
+}
+
+
+/* NOTE:  DaVinci autoreq is ignored except for host side "RNDIS" mode RX;
+ * so we won't ever use it (see "CPPI RX Woes" below).
+ */
+static inline int cppi_autoreq_update(struct cppi_channel *rx,
+		void __iomem *tibase, int onepacket, unsigned n_bds)
+{
+	u32	val;
+
+#ifdef	RNDIS_RX_IS_USABLE
+	u32	tmp;
+	/* assert(is_host_active(musb)) */
+
+	/* start from "AutoReq never" */
+	tmp = musb_readl(tibase, DAVINCI_AUTOREQ_REG);
+	val = tmp & ~((0x3) << (rx->index * 2));
+
+	/* HCD arranged reqpkt for packet #1.  we arrange int
+	 * for all but the last one, maybe in two segments.
+	 */
+	if (!onepacket) {
+#if 0
+		/* use two segments, autoreq "all" then the last "never" */
+		val |= ((0x3) << (rx->index * 2));
+		n_bds--;
+#else
+		/* one segment, autoreq "all-but-last" */
+		val |= ((0x1) << (rx->index * 2));
+#endif
+	}
+
+	if (val != tmp) {
+		int n = 100;
+
+		/* make sure that autoreq is updated before continuing */
+		musb_writel(tibase, DAVINCI_AUTOREQ_REG, val);
+		do {
+			tmp = musb_readl(tibase, DAVINCI_AUTOREQ_REG);
+			if (tmp == val)
+				break;
+			cpu_relax();
+		} while (n-- > 0);
+	}
+#endif
+
+	/* REQPKT is turned off after each segment */
+	if (n_bds && rx->channel.actual_len) {
+		void __iomem	*regs = rx->hw_ep->regs;
+
+		val = musb_readw(regs, MUSB_RXCSR);
+		if (!(val & MUSB_RXCSR_H_REQPKT)) {
+			val |= MUSB_RXCSR_H_REQPKT | MUSB_RXCSR_H_WZC_BITS;
+			musb_writew(regs, MUSB_RXCSR, val);
+			/* flush writebuffer */
+			val = musb_readw(regs, MUSB_RXCSR);
+		}
+	}
+	return n_bds;
+}
+
+
+/* Buffer enqueuing Logic:
+ *
+ *  - RX builds new queues each time, to help handle routine "early
+ *    termination" cases (faults, including errors and short reads)
+ *    more correctly.
+ *
+ *  - for now, TX reuses the same queue of BDs every time
+ *
+ * REVISIT long term, we want a normal dynamic model.
+ * ... the goal will be to append to the
+ * existing queue, processing completed "dma buffers" (segments) on the fly.
+ *
+ * Otherwise we force an IRQ latency between requests, which slows us a lot
+ * (especially in "transparent" dma).  Unfortunately that model seems to be
+ * inherent in the DMA model from the Mentor code, except in the rare case
+ * of transfers big enough (~128+ KB) that we could append "middle" segments
+ * in the TX paths.  (RX can't do this, see below.)
+ *
+ * That's true even in the CPPI- friendly iso case, where most urbs have
+ * several small segments provided in a group and where the "packet at a time"
+ * "transparent" DMA model is always correct, even on the RX side.
+ */
+
+/*
+ * CPPI TX:
+ * ========
+ * TX is a lot more reasonable than RX; it doesn't need to run in
+ * irq-per-packet mode very often.  RNDIS mode seems to behave too
+ * (except how it handles the exactly-N-packets case).  Building a
+ * txdma queue with multiple requests (urb or usb_request) looks
+ * like it would work ... but fault handling would need much testing.
+ *
+ * The main issue with TX mode RNDIS relates to transfer lengths that
+ * are an exact multiple of the packet length.  It appears that there's
+ * a hiccup in that case (maybe the DMA completes before the ZLP gets
+ * written?) boiling down to not being able to rely on CPPI writing any
+ * terminating zero length packet before the next transfer is written.
+ * So that's punted to PIO; better yet, gadget drivers can avoid it.
+ *
+ * Plus, there's allegedly an undocumented constraint that rndis transfer
+ * length be a multiple of 64 bytes ... but the chip doesn't act that
+ * way, and we really don't _want_ that behavior anyway.
+ *
+ * On TX, "transparent" mode works ... although experiments have shown
+ * problems trying to use the SOP/EOP bits in different USB packets.
+ *
+ * REVISIT try to handle terminating zero length packets using CPPI
+ * instead of doing it by PIO after an IRQ.  (Meanwhile, make Ethernet
+ * links avoid that issue by forcing them to avoid zlps.)
+ */
+static void
+cppi_next_tx_segment(struct musb *musb, struct cppi_channel *tx)
+{
+	unsigned		maxpacket = tx->maxpacket;
+	dma_addr_t		addr = tx->buf_dma + tx->offset;
+	size_t			length = tx->buf_len - tx->offset;
+	struct cppi_descriptor	*bd;
+	unsigned		n_bds;
+	unsigned		i;
+	struct cppi_tx_stateram	__iomem *tx_ram = tx->state_ram;
+	int			rndis;
+
+	/* TX can use the CPPI "rndis" mode, where we can probably fit this
+	 * transfer in one BD and one IRQ.  The only time we would NOT want
+	 * to use it is when hardware constraints prevent it, or if we'd
+	 * trigger the "send a ZLP?" confusion.
+	 */
+	rndis = (maxpacket & 0x3f) == 0
+		&& length > maxpacket
+		&& length < 0xffff
+		&& (length % maxpacket) != 0;
+
+	if (rndis) {
+		maxpacket = length;
+		n_bds = 1;
+	} else {
+		if (length)
+			n_bds = DIV_ROUND_UP(length, maxpacket);
+		else
+			n_bds = 1;
+		n_bds = min(n_bds, (unsigned) NUM_TXCHAN_BD);
+		length = min(n_bds * maxpacket, length);
+	}
+
+	musb_dbg(musb, "TX DMA%d, pktSz %d %s bds %d dma 0x%llx len %u",
+			tx->index,
+			maxpacket,
+			rndis ? "rndis" : "transparent",
+			n_bds,
+			(unsigned long long)addr, length);
+
+	cppi_rndis_update(tx, 0, musb->ctrl_base, rndis);
+
+	/* assuming here that channel_program is called during
+	 * transfer initiation ... current code maintains state
+	 * for one outstanding request only (no queues, not even
+	 * the implicit ones of an iso urb).
+	 */
+
+	bd = tx->freelist;
+	tx->head = bd;
+	tx->last_processed = NULL;
+
+	/* FIXME use BD pool like RX side does, and just queue
+	 * the minimum number for this request.
+	 */
+
+	/* Prepare queue of BDs first, then hand it to hardware.
+	 * All BDs except maybe the last should be of full packet
+	 * size; for RNDIS there _is_ only that last packet.
+	 */
+	for (i = 0; i < n_bds; ) {
+		if (++i < n_bds && bd->next)
+			bd->hw_next = bd->next->dma;
+		else
+			bd->hw_next = 0;
+
+		bd->hw_bufp = tx->buf_dma + tx->offset;
+
+		/* FIXME set EOP only on the last packet,
+		 * SOP only on the first ... avoid IRQs
+		 */
+		if ((tx->offset + maxpacket) <= tx->buf_len) {
+			tx->offset += maxpacket;
+			bd->hw_off_len = maxpacket;
+			bd->hw_options = CPPI_SOP_SET | CPPI_EOP_SET
+				| CPPI_OWN_SET | maxpacket;
+		} else {
+			/* only this one may be a partial USB Packet */
+			u32		partial_len;
+
+			partial_len = tx->buf_len - tx->offset;
+			tx->offset = tx->buf_len;
+			bd->hw_off_len = partial_len;
+
+			bd->hw_options = CPPI_SOP_SET | CPPI_EOP_SET
+				| CPPI_OWN_SET | partial_len;
+			if (partial_len == 0)
+				bd->hw_options |= CPPI_ZERO_SET;
+		}
+
+		musb_dbg(musb, "TXBD %p: nxt %08x buf %08x len %04x opt %08x",
+				bd, bd->hw_next, bd->hw_bufp,
+				bd->hw_off_len, bd->hw_options);
+
+		/* update the last BD enqueued to the list */
+		tx->tail = bd;
+		bd = bd->next;
+	}
+
+	/* BDs live in DMA-coherent memory, but writes might be pending */
+	cpu_drain_writebuffer();
+
+	/* Write to the HeadPtr in state RAM to trigger */
+	musb_writel(&tx_ram->tx_head, 0, (u32)tx->freelist->dma);
+
+	cppi_dump_tx(5, tx, "/S");
+}
+
+/*
+ * CPPI RX Woes:
+ * =============
+ * Consider a 1KB bulk RX buffer in two scenarios:  (a) it's fed two 300 byte
+ * packets back-to-back, and (b) it's fed two 512 byte packets back-to-back.
+ * (Full speed transfers have similar scenarios.)
+ *
+ * The correct behavior for Linux is that (a) fills the buffer with 300 bytes,
+ * and the next packet goes into a buffer that's queued later; while (b) fills
+ * the buffer with 1024 bytes.  How to do that with CPPI?
+ *
+ * - RX queues in "rndis" mode -- one single BD -- handle (a) correctly, but
+ *   (b) loses **BADLY** because nothing (!) happens when that second packet
+ *   fills the buffer, much less when a third one arrives.  (Which makes this
+ *   not a "true" RNDIS mode.  In the RNDIS protocol short-packet termination
+ *   is optional, and it's fine if peripherals -- not hosts! -- pad messages
+ *   out to end-of-buffer.  Standard PCI host controller DMA descriptors
+ *   implement that mode by default ... which is no accident.)
+ *
+ * - RX queues in "transparent" mode -- two BDs with 512 bytes each -- have
+ *   converse problems:  (b) is handled right, but (a) loses badly.  CPPI RX
+ *   ignores SOP/EOP markings and processes both of those BDs; so both packets
+ *   are loaded into the buffer (with a 212 byte gap between them), and the next
+ *   buffer queued will NOT get its 300 bytes of data. (It seems like SOP/EOP
+ *   are intended as outputs for RX queues, not inputs...)
+ *
+ * - A variant of "transparent" mode -- one BD at a time -- is the only way to
+ *   reliably make both cases work, with software handling both cases correctly
+ *   and at the significant penalty of needing an IRQ per packet.  (The lack of
+ *   I/O overlap can be slightly ameliorated by enabling double buffering.)
+ *
+ * So how to get rid of IRQ-per-packet?  The transparent multi-BD case could
+ * be used in special cases like mass storage, which sets URB_SHORT_NOT_OK
+ * (or maybe its peripheral side counterpart) to flag (a) scenarios as errors
+ * with guaranteed driver level fault recovery and scrubbing out what's left
+ * of that garbaged datastream.
+ *
+ * But there seems to be no way to identify the cases where CPPI RNDIS mode
+ * is appropriate -- which do NOT include RNDIS host drivers, but do include
+ * the CDC Ethernet driver! -- and the documentation is incomplete/wrong.
+ * So we can't _ever_ use RX RNDIS mode ... except by using a heuristic
+ * that applies best on the peripheral side (and which could fail rudely).
+ *
+ * Leaving only "transparent" mode; we avoid multi-bd modes in almost all
+ * cases other than mass storage class.  Otherwise we're correct but slow,
+ * since CPPI penalizes our need for a "true RNDIS" default mode.
+ */
+
+
+/* Heuristic, intended to kick in for ethernet/rndis peripheral ONLY
+ *
+ * IFF
+ *  (a)	peripheral mode ... since rndis peripherals could pad their
+ *	writes to hosts, causing i/o failure; or we'd have to cope with
+ *	a largely unknowable variety of host side protocol variants
+ *  (b)	and short reads are NOT errors ... since full reads would
+ *	cause those same i/o failures
+ *  (c)	and read length is
+ *	- less than 64KB (max per cppi descriptor)
+ *	- not a multiple of 4096 (g_zero default, full reads typical)
+ *	- N (>1) packets long, ditto (full reads not EXPECTED)
+ * THEN
+ *   try rx rndis mode
+ *
+ * Cost of heuristic failing:  RXDMA wedges at the end of transfers that
+ * fill out the whole buffer.  Buggy host side usb network drivers could
+ * trigger that, but "in the field" such bugs seem to be all but unknown.
+ *
+ * So this module parameter lets the heuristic be disabled.  When using
+ * gadgetfs, the heuristic will probably need to be disabled.
+ */
+static bool cppi_rx_rndis = 1;
+
+module_param(cppi_rx_rndis, bool, 0);
+MODULE_PARM_DESC(cppi_rx_rndis, "enable/disable RX RNDIS heuristic");
+
+
+/**
+ * cppi_next_rx_segment - dma read for the next chunk of a buffer
+ * @musb: the controller
+ * @rx: dma channel
+ * @onepacket: true unless caller treats short reads as errors, and
+ *	performs fault recovery above usbcore.
+ * Context: controller irqlocked
+ *
+ * See above notes about why we can't use multi-BD RX queues except in
+ * rare cases (mass storage class), and can never use the hardware "rndis"
+ * mode (since it's not a "true" RNDIS mode) with complete safety..
+ *
+ * It's ESSENTIAL that callers specify "onepacket" mode unless they kick in
+ * code to recover from corrupted datastreams after each short transfer.
+ */
+static void
+cppi_next_rx_segment(struct musb *musb, struct cppi_channel *rx, int onepacket)
+{
+	unsigned		maxpacket = rx->maxpacket;
+	dma_addr_t		addr = rx->buf_dma + rx->offset;
+	size_t			length = rx->buf_len - rx->offset;
+	struct cppi_descriptor	*bd, *tail;
+	unsigned		n_bds;
+	unsigned		i;
+	void __iomem		*tibase = musb->ctrl_base;
+	int			is_rndis = 0;
+	struct cppi_rx_stateram	__iomem *rx_ram = rx->state_ram;
+	struct cppi_descriptor	*d;
+
+	if (onepacket) {
+		/* almost every USB driver, host or peripheral side */
+		n_bds = 1;
+
+		/* maybe apply the heuristic above */
+		if (cppi_rx_rndis
+				&& is_peripheral_active(musb)
+				&& length > maxpacket
+				&& (length & ~0xffff) == 0
+				&& (length & 0x0fff) != 0
+				&& (length & (maxpacket - 1)) == 0) {
+			maxpacket = length;
+			is_rndis = 1;
+		}
+	} else {
+		/* virtually nothing except mass storage class */
+		if (length > 0xffff) {
+			n_bds = 0xffff / maxpacket;
+			length = n_bds * maxpacket;
+		} else {
+			n_bds = DIV_ROUND_UP(length, maxpacket);
+		}
+		if (n_bds == 1)
+			onepacket = 1;
+		else
+			n_bds = min(n_bds, (unsigned) NUM_RXCHAN_BD);
+	}
+
+	/* In host mode, autorequest logic can generate some IN tokens; it's
+	 * tricky since we can't leave REQPKT set in RXCSR after the transfer
+	 * finishes. So:  multipacket transfers involve two or more segments.
+	 * And always at least two IRQs ... RNDIS mode is not an option.
+	 */
+	if (is_host_active(musb))
+		n_bds = cppi_autoreq_update(rx, tibase, onepacket, n_bds);
+
+	cppi_rndis_update(rx, 1, musb->ctrl_base, is_rndis);
+
+	length = min(n_bds * maxpacket, length);
+
+	musb_dbg(musb, "RX DMA%d seg, maxp %d %s bds %d (cnt %d) "
+			"dma 0x%llx len %u %u/%u",
+			rx->index, maxpacket,
+			onepacket
+				? (is_rndis ? "rndis" : "onepacket")
+				: "multipacket",
+			n_bds,
+			musb_readl(tibase,
+				DAVINCI_RXCPPI_BUFCNT0_REG + (rx->index * 4))
+					& 0xffff,
+			(unsigned long long)addr, length,
+			rx->channel.actual_len, rx->buf_len);
+
+	/* only queue one segment at a time, since the hardware prevents
+	 * correct queue shutdown after unexpected short packets
+	 */
+	bd = cppi_bd_alloc(rx);
+	rx->head = bd;
+
+	/* Build BDs for all packets in this segment */
+	for (i = 0, tail = NULL; bd && i < n_bds; i++, tail = bd) {
+		u32	bd_len;
+
+		if (i) {
+			bd = cppi_bd_alloc(rx);
+			if (!bd)
+				break;
+			tail->next = bd;
+			tail->hw_next = bd->dma;
+		}
+		bd->hw_next = 0;
+
+		/* all but the last packet will be maxpacket size */
+		if (maxpacket < length)
+			bd_len = maxpacket;
+		else
+			bd_len = length;
+
+		bd->hw_bufp = addr;
+		addr += bd_len;
+		rx->offset += bd_len;
+
+		bd->hw_off_len = (0 /*offset*/ << 16) + bd_len;
+		bd->buflen = bd_len;
+
+		bd->hw_options = CPPI_OWN_SET | (i == 0 ? length : 0);
+		length -= bd_len;
+	}
+
+	/* we always expect at least one reusable BD! */
+	if (!tail) {
+		WARNING("rx dma%d -- no BDs? need %d\n", rx->index, n_bds);
+		return;
+	} else if (i < n_bds)
+		WARNING("rx dma%d -- only %d of %d BDs\n", rx->index, i, n_bds);
+
+	tail->next = NULL;
+	tail->hw_next = 0;
+
+	bd = rx->head;
+	rx->tail = tail;
+
+	/* short reads and other faults should terminate this entire
+	 * dma segment.  we want one "dma packet" per dma segment, not
+	 * one per USB packet, terminating the whole queue at once...
+	 * NOTE that current hardware seems to ignore SOP and EOP.
+	 */
+	bd->hw_options |= CPPI_SOP_SET;
+	tail->hw_options |= CPPI_EOP_SET;
+
+	for (d = rx->head; d; d = d->next)
+		cppi_dump_rxbd("S", d);
+
+	/* in case the preceding transfer left some state... */
+	tail = rx->last_processed;
+	if (tail) {
+		tail->next = bd;
+		tail->hw_next = bd->dma;
+	}
+
+	core_rxirq_enable(tibase, rx->index + 1);
+
+	/* BDs live in DMA-coherent memory, but writes might be pending */
+	cpu_drain_writebuffer();
+
+	/* REVISIT specs say to write this AFTER the BUFCNT register
+	 * below ... but that loses badly.
+	 */
+	musb_writel(&rx_ram->rx_head, 0, bd->dma);
+
+	/* bufferCount must be at least 3, and zeroes on completion
+	 * unless it underflows below zero, or stops at two, or keeps
+	 * growing ... grr.
+	 */
+	i = musb_readl(tibase,
+			DAVINCI_RXCPPI_BUFCNT0_REG + (rx->index * 4))
+			& 0xffff;
+
+	if (!i)
+		musb_writel(tibase,
+			DAVINCI_RXCPPI_BUFCNT0_REG + (rx->index * 4),
+			n_bds + 2);
+	else if (n_bds > (i - 3))
+		musb_writel(tibase,
+			DAVINCI_RXCPPI_BUFCNT0_REG + (rx->index * 4),
+			n_bds - (i - 3));
+
+	i = musb_readl(tibase,
+			DAVINCI_RXCPPI_BUFCNT0_REG + (rx->index * 4))
+			& 0xffff;
+	if (i < (2 + n_bds)) {
+		musb_dbg(musb, "bufcnt%d underrun - %d (for %d)",
+					rx->index, i, n_bds);
+		musb_writel(tibase,
+			DAVINCI_RXCPPI_BUFCNT0_REG + (rx->index * 4),
+			n_bds + 2);
+	}
+
+	cppi_dump_rx(4, rx, "/S");
+}
+
+/**
+ * cppi_channel_program - program channel for data transfer
+ * @ch: the channel
+ * @maxpacket: max packet size
+ * @mode: For RX, 1 unless the usb protocol driver promised to treat
+ *	all short reads as errors and kick in high level fault recovery.
+ *	For TX, ignored because of RNDIS mode races/glitches.
+ * @dma_addr: dma address of buffer
+ * @len: length of buffer
+ * Context: controller irqlocked
+ */
+static int cppi_channel_program(struct dma_channel *ch,
+		u16 maxpacket, u8 mode,
+		dma_addr_t dma_addr, u32 len)
+{
+	struct cppi_channel	*cppi_ch;
+	struct cppi		*controller;
+	struct musb		*musb;
+
+	cppi_ch = container_of(ch, struct cppi_channel, channel);
+	controller = cppi_ch->controller;
+	musb = controller->controller.musb;
+
+	switch (ch->status) {
+	case MUSB_DMA_STATUS_BUS_ABORT:
+	case MUSB_DMA_STATUS_CORE_ABORT:
+		/* fault irq handler should have handled cleanup */
+		WARNING("%cX DMA%d not cleaned up after abort!\n",
+				cppi_ch->transmit ? 'T' : 'R',
+				cppi_ch->index);
+		/* WARN_ON(1); */
+		break;
+	case MUSB_DMA_STATUS_BUSY:
+		WARNING("program active channel?  %cX DMA%d\n",
+				cppi_ch->transmit ? 'T' : 'R',
+				cppi_ch->index);
+		/* WARN_ON(1); */
+		break;
+	case MUSB_DMA_STATUS_UNKNOWN:
+		musb_dbg(musb, "%cX DMA%d not allocated!",
+				cppi_ch->transmit ? 'T' : 'R',
+				cppi_ch->index);
+		fallthrough;
+	case MUSB_DMA_STATUS_FREE:
+		break;
+	}
+
+	ch->status = MUSB_DMA_STATUS_BUSY;
+
+	/* set transfer parameters, then queue up its first segment */
+	cppi_ch->buf_dma = dma_addr;
+	cppi_ch->offset = 0;
+	cppi_ch->maxpacket = maxpacket;
+	cppi_ch->buf_len = len;
+	cppi_ch->channel.actual_len = 0;
+
+	/* TX channel? or RX? */
+	if (cppi_ch->transmit)
+		cppi_next_tx_segment(musb, cppi_ch);
+	else
+		cppi_next_rx_segment(musb, cppi_ch, mode);
+
+	return true;
+}
+
+static bool cppi_rx_scan(struct cppi *cppi, unsigned ch)
+{
+	struct cppi_channel		*rx = &cppi->rx[ch];
+	struct cppi_rx_stateram __iomem	*state = rx->state_ram;
+	struct cppi_descriptor		*bd;
+	struct cppi_descriptor		*last = rx->last_processed;
+	bool				completed = false;
+	bool				acked = false;
+	int				i;
+	dma_addr_t			safe2ack;
+	void __iomem			*regs = rx->hw_ep->regs;
+	struct musb			*musb = cppi->controller.musb;
+
+	cppi_dump_rx(6, rx, "/K");
+
+	bd = last ? last->next : rx->head;
+	if (!bd)
+		return false;
+
+	/* run through all completed BDs */
+	for (i = 0, safe2ack = musb_readl(&state->rx_complete, 0);
+			(safe2ack || completed) && bd && i < NUM_RXCHAN_BD;
+			i++, bd = bd->next) {
+		u16	len;
+
+		/* catch latest BD writes from CPPI */
+		rmb();
+		if (!completed && (bd->hw_options & CPPI_OWN_SET))
+			break;
+
+		musb_dbg(musb, "C/RXBD %llx: nxt %08x buf %08x "
+			"off.len %08x opt.len %08x (%d)",
+			(unsigned long long)bd->dma, bd->hw_next, bd->hw_bufp,
+			bd->hw_off_len, bd->hw_options,
+			rx->channel.actual_len);
+
+		/* actual packet received length */
+		if ((bd->hw_options & CPPI_SOP_SET) && !completed)
+			len = bd->hw_off_len & CPPI_RECV_PKTLEN_MASK;
+		else
+			len = 0;
+
+		if (bd->hw_options & CPPI_EOQ_MASK)
+			completed = true;
+
+		if (!completed && len < bd->buflen) {
+			/* NOTE:  when we get a short packet, RXCSR_H_REQPKT
+			 * must have been cleared, and no more DMA packets may
+			 * active be in the queue... TI docs didn't say, but
+			 * CPPI ignores those BDs even though OWN is still set.
+			 */
+			completed = true;
+			musb_dbg(musb, "rx short %d/%d (%d)",
+					len, bd->buflen,
+					rx->channel.actual_len);
+		}
+
+		/* If we got here, we expect to ack at least one BD; meanwhile
+		 * CPPI may completing other BDs while we scan this list...
+		 *
+		 * RACE: we can notice OWN cleared before CPPI raises the
+		 * matching irq by writing that BD as the completion pointer.
+		 * In such cases, stop scanning and wait for the irq, avoiding
+		 * lost acks and states where BD ownership is unclear.
+		 */
+		if (bd->dma == safe2ack) {
+			musb_writel(&state->rx_complete, 0, safe2ack);
+			safe2ack = musb_readl(&state->rx_complete, 0);
+			acked = true;
+			if (bd->dma == safe2ack)
+				safe2ack = 0;
+		}
+
+		rx->channel.actual_len += len;
+
+		cppi_bd_free(rx, last);
+		last = bd;
+
+		/* stop scanning on end-of-segment */
+		if (bd->hw_next == 0)
+			completed = true;
+	}
+	rx->last_processed = last;
+
+	/* dma abort, lost ack, or ... */
+	if (!acked && last) {
+		int	csr;
+
+		if (safe2ack == 0 || safe2ack == rx->last_processed->dma)
+			musb_writel(&state->rx_complete, 0, safe2ack);
+		if (safe2ack == 0) {
+			cppi_bd_free(rx, last);
+			rx->last_processed = NULL;
+
+			/* if we land here on the host side, H_REQPKT will
+			 * be clear and we need to restart the queue...
+			 */
+			WARN_ON(rx->head);
+		}
+		musb_ep_select(cppi->mregs, rx->index + 1);
+		csr = musb_readw(regs, MUSB_RXCSR);
+		if (csr & MUSB_RXCSR_DMAENAB) {
+			musb_dbg(musb, "list%d %p/%p, last %llx%s, csr %04x",
+				rx->index,
+				rx->head, rx->tail,
+				rx->last_processed
+					? (unsigned long long)
+						rx->last_processed->dma
+					: 0,
+				completed ? ", completed" : "",
+				csr);
+			cppi_dump_rxq(4, "/what?", rx);
+		}
+	}
+	if (!completed) {
+		int	csr;
+
+		rx->head = bd;
+
+		/* REVISIT seems like "autoreq all but EOP" doesn't...
+		 * setting it here "should" be racey, but seems to work
+		 */
+		csr = musb_readw(rx->hw_ep->regs, MUSB_RXCSR);
+		if (is_host_active(cppi->controller.musb)
+				&& bd
+				&& !(csr & MUSB_RXCSR_H_REQPKT)) {
+			csr |= MUSB_RXCSR_H_REQPKT;
+			musb_writew(regs, MUSB_RXCSR,
+					MUSB_RXCSR_H_WZC_BITS | csr);
+			csr = musb_readw(rx->hw_ep->regs, MUSB_RXCSR);
+		}
+	} else {
+		rx->head = NULL;
+		rx->tail = NULL;
+	}
+
+	cppi_dump_rx(6, rx, completed ? "/completed" : "/cleaned");
+	return completed;
+}
+
+irqreturn_t cppi_interrupt(int irq, void *dev_id)
+{
+	struct musb		*musb = dev_id;
+	struct cppi		*cppi;
+	void __iomem		*tibase;
+	struct musb_hw_ep	*hw_ep = NULL;
+	u32			rx, tx;
+	int			i, index;
+	unsigned long		flags;
+
+	cppi = container_of(musb->dma_controller, struct cppi, controller);
+	if (cppi->irq)
+		spin_lock_irqsave(&musb->lock, flags);
+
+	tibase = musb->ctrl_base;
+
+	tx = musb_readl(tibase, DAVINCI_TXCPPI_MASKED_REG);
+	rx = musb_readl(tibase, DAVINCI_RXCPPI_MASKED_REG);
+
+	if (!tx && !rx) {
+		if (cppi->irq)
+			spin_unlock_irqrestore(&musb->lock, flags);
+		return IRQ_NONE;
+	}
+
+	musb_dbg(musb, "CPPI IRQ Tx%x Rx%x", tx, rx);
+
+	/* process TX channels */
+	for (index = 0; tx; tx = tx >> 1, index++) {
+		struct cppi_channel		*tx_ch;
+		struct cppi_tx_stateram __iomem	*tx_ram;
+		bool				completed = false;
+		struct cppi_descriptor		*bd;
+
+		if (!(tx & 1))
+			continue;
+
+		tx_ch = cppi->tx + index;
+		tx_ram = tx_ch->state_ram;
+
+		/* FIXME  need a cppi_tx_scan() routine, which
+		 * can also be called from abort code
+		 */
+
+		cppi_dump_tx(5, tx_ch, "/E");
+
+		bd = tx_ch->head;
+
+		/*
+		 * If Head is null then this could mean that a abort interrupt
+		 * that needs to be acknowledged.
+		 */
+		if (NULL == bd) {
+			musb_dbg(musb, "null BD");
+			musb_writel(&tx_ram->tx_complete, 0, 0);
+			continue;
+		}
+
+		/* run through all completed BDs */
+		for (i = 0; !completed && bd && i < NUM_TXCHAN_BD;
+				i++, bd = bd->next) {
+			u16	len;
+
+			/* catch latest BD writes from CPPI */
+			rmb();
+			if (bd->hw_options & CPPI_OWN_SET)
+				break;
+
+			musb_dbg(musb, "C/TXBD %p n %x b %x off %x opt %x",
+					bd, bd->hw_next, bd->hw_bufp,
+					bd->hw_off_len, bd->hw_options);
+
+			len = bd->hw_off_len & CPPI_BUFFER_LEN_MASK;
+			tx_ch->channel.actual_len += len;
+
+			tx_ch->last_processed = bd;
+
+			/* write completion register to acknowledge
+			 * processing of completed BDs, and possibly
+			 * release the IRQ; EOQ might not be set ...
+			 *
+			 * REVISIT use the same ack strategy as rx
+			 *
+			 * REVISIT have observed bit 18 set; huh??
+			 */
+			/* if ((bd->hw_options & CPPI_EOQ_MASK)) */
+				musb_writel(&tx_ram->tx_complete, 0, bd->dma);
+
+			/* stop scanning on end-of-segment */
+			if (bd->hw_next == 0)
+				completed = true;
+		}
+
+		/* on end of segment, maybe go to next one */
+		if (completed) {
+			/* cppi_dump_tx(4, tx_ch, "/complete"); */
+
+			/* transfer more, or report completion */
+			if (tx_ch->offset >= tx_ch->buf_len) {
+				tx_ch->head = NULL;
+				tx_ch->tail = NULL;
+				tx_ch->channel.status = MUSB_DMA_STATUS_FREE;
+
+				hw_ep = tx_ch->hw_ep;
+
+				musb_dma_completion(musb, index + 1, 1);
+
+			} else {
+				/* Bigger transfer than we could fit in
+				 * that first batch of descriptors...
+				 */
+				cppi_next_tx_segment(musb, tx_ch);
+			}
+		} else
+			tx_ch->head = bd;
+	}
+
+	/* Start processing the RX block */
+	for (index = 0; rx; rx = rx >> 1, index++) {
+
+		if (rx & 1) {
+			struct cppi_channel		*rx_ch;
+
+			rx_ch = cppi->rx + index;
+
+			/* let incomplete dma segments finish */
+			if (!cppi_rx_scan(cppi, index))
+				continue;
+
+			/* start another dma segment if needed */
+			if (rx_ch->channel.actual_len != rx_ch->buf_len
+					&& rx_ch->channel.actual_len
+						== rx_ch->offset) {
+				cppi_next_rx_segment(musb, rx_ch, 1);
+				continue;
+			}
+
+			/* all segments completed! */
+			rx_ch->channel.status = MUSB_DMA_STATUS_FREE;
+
+			hw_ep = rx_ch->hw_ep;
+
+			core_rxirq_disable(tibase, index + 1);
+			musb_dma_completion(musb, index + 1, 0);
+		}
+	}
+
+	/* write to CPPI EOI register to re-enable interrupts */
+	musb_writel(tibase, DAVINCI_CPPI_EOI_REG, 0);
+
+	if (cppi->irq)
+		spin_unlock_irqrestore(&musb->lock, flags);
+
+	return IRQ_HANDLED;
+}
+EXPORT_SYMBOL_GPL(cppi_interrupt);
+
+/* Instantiate a software object representing a DMA controller. */
+struct dma_controller *
+cppi_dma_controller_create(struct musb *musb, void __iomem *mregs)
+{
+	struct cppi		*controller;
+	struct device		*dev = musb->controller;
+	struct platform_device	*pdev = to_platform_device(dev);
+	int			irq = platform_get_irq_byname(pdev, "dma");
+
+	controller = kzalloc(sizeof *controller, GFP_KERNEL);
+	if (!controller)
+		return NULL;
+
+	controller->mregs = mregs;
+	controller->tibase = mregs - DAVINCI_BASE_OFFSET;
+
+	controller->controller.musb = musb;
+	controller->controller.channel_alloc = cppi_channel_allocate;
+	controller->controller.channel_release = cppi_channel_release;
+	controller->controller.channel_program = cppi_channel_program;
+	controller->controller.channel_abort = cppi_channel_abort;
+
+	/* NOTE: allocating from on-chip SRAM would give the least
+	 * contention for memory access, if that ever matters here.
+	 */
+
+	/* setup BufferPool */
+	controller->pool = dma_pool_create("cppi",
+			controller->controller.musb->controller,
+			sizeof(struct cppi_descriptor),
+			CPPI_DESCRIPTOR_ALIGN, 0);
+	if (!controller->pool) {
+		kfree(controller);
+		return NULL;
+	}
+
+	if (irq > 0) {
+		if (request_irq(irq, cppi_interrupt, 0, "cppi-dma", musb)) {
+			dev_err(dev, "request_irq %d failed!\n", irq);
+			musb_dma_controller_destroy(&controller->controller);
+			return NULL;
+		}
+		controller->irq = irq;
+	}
+
+	cppi_controller_start(controller);
+	return &controller->controller;
+}
+EXPORT_SYMBOL_GPL(cppi_dma_controller_create);
+
+/*
+ *  Destroy a previously-instantiated DMA controller.
+ */
+void cppi_dma_controller_destroy(struct dma_controller *c)
+{
+	struct cppi	*cppi;
+
+	cppi = container_of(c, struct cppi, controller);
+
+	cppi_controller_stop(cppi);
+
+	if (cppi->irq)
+		free_irq(cppi->irq, cppi->controller.musb);
+
+	/* assert:  caller stopped the controller first */
+	dma_pool_destroy(cppi->pool);
+
+	kfree(cppi);
+}
+EXPORT_SYMBOL_GPL(cppi_dma_controller_destroy);
+
+/*
+ * Context: controller irqlocked, endpoint selected
+ */
+static int cppi_channel_abort(struct dma_channel *channel)
+{
+	struct cppi_channel	*cppi_ch;
+	struct cppi		*controller;
+	void __iomem		*mbase;
+	void __iomem		*tibase;
+	void __iomem		*regs;
+	u32			value;
+	struct cppi_descriptor	*queue;
+
+	cppi_ch = container_of(channel, struct cppi_channel, channel);
+
+	controller = cppi_ch->controller;
+
+	switch (channel->status) {
+	case MUSB_DMA_STATUS_BUS_ABORT:
+	case MUSB_DMA_STATUS_CORE_ABORT:
+		/* from RX or TX fault irq handler */
+	case MUSB_DMA_STATUS_BUSY:
+		/* the hardware needs shutting down */
+		regs = cppi_ch->hw_ep->regs;
+		break;
+	case MUSB_DMA_STATUS_UNKNOWN:
+	case MUSB_DMA_STATUS_FREE:
+		return 0;
+	default:
+		return -EINVAL;
+	}
+
+	if (!cppi_ch->transmit && cppi_ch->head)
+		cppi_dump_rxq(3, "/abort", cppi_ch);
+
+	mbase = controller->mregs;
+	tibase = controller->tibase;
+
+	queue = cppi_ch->head;
+	cppi_ch->head = NULL;
+	cppi_ch->tail = NULL;
+
+	/* REVISIT should rely on caller having done this,
+	 * and caller should rely on us not changing it.
+	 * peripheral code is safe ... check host too.
+	 */
+	musb_ep_select(mbase, cppi_ch->index + 1);
+
+	if (cppi_ch->transmit) {
+		struct cppi_tx_stateram __iomem *tx_ram;
+		/* REVISIT put timeouts on these controller handshakes */
+
+		cppi_dump_tx(6, cppi_ch, " (teardown)");
+
+		/* teardown DMA engine then usb core */
+		do {
+			value = musb_readl(tibase, DAVINCI_TXCPPI_TEAR_REG);
+		} while (!(value & CPPI_TEAR_READY));
+		musb_writel(tibase, DAVINCI_TXCPPI_TEAR_REG, cppi_ch->index);
+
+		tx_ram = cppi_ch->state_ram;
+		do {
+			value = musb_readl(&tx_ram->tx_complete, 0);
+		} while (0xFFFFFFFC != value);
+
+		/* FIXME clean up the transfer state ... here?
+		 * the completion routine should get called with
+		 * an appropriate status code.
+		 */
+
+		value = musb_readw(regs, MUSB_TXCSR);
+		value &= ~MUSB_TXCSR_DMAENAB;
+		value |= MUSB_TXCSR_FLUSHFIFO;
+		musb_writew(regs, MUSB_TXCSR, value);
+		musb_writew(regs, MUSB_TXCSR, value);
+
+		/*
+		 * 1. Write to completion Ptr value 0x1(bit 0 set)
+		 *    (write back mode)
+		 * 2. Wait for abort interrupt and then put the channel in
+		 *    compare mode by writing 1 to the tx_complete register.
+		 */
+		cppi_reset_tx(tx_ram, 1);
+		cppi_ch->head = NULL;
+		musb_writel(&tx_ram->tx_complete, 0, 1);
+		cppi_dump_tx(5, cppi_ch, " (done teardown)");
+
+		/* REVISIT tx side _should_ clean up the same way
+		 * as the RX side ... this does no cleanup at all!
+		 */
+
+	} else /* RX */ {
+		u16			csr;
+
+		/* NOTE: docs don't guarantee any of this works ...  we
+		 * expect that if the usb core stops telling the cppi core
+		 * to pull more data from it, then it'll be safe to flush
+		 * current RX DMA state iff any pending fifo transfer is done.
+		 */
+
+		core_rxirq_disable(tibase, cppi_ch->index + 1);
+
+		/* for host, ensure ReqPkt is never set again */
+		if (is_host_active(cppi_ch->controller->controller.musb)) {
+			value = musb_readl(tibase, DAVINCI_AUTOREQ_REG);
+			value &= ~((0x3) << (cppi_ch->index * 2));
+			musb_writel(tibase, DAVINCI_AUTOREQ_REG, value);
+		}
+
+		csr = musb_readw(regs, MUSB_RXCSR);
+
+		/* for host, clear (just) ReqPkt at end of current packet(s) */
+		if (is_host_active(cppi_ch->controller->controller.musb)) {
+			csr |= MUSB_RXCSR_H_WZC_BITS;
+			csr &= ~MUSB_RXCSR_H_REQPKT;
+		} else
+			csr |= MUSB_RXCSR_P_WZC_BITS;
+
+		/* clear dma enable */
+		csr &= ~(MUSB_RXCSR_DMAENAB);
+		musb_writew(regs, MUSB_RXCSR, csr);
+		csr = musb_readw(regs, MUSB_RXCSR);
+
+		/* Quiesce: wait for current dma to finish (if not cleanup).
+		 * We can't use bit zero of stateram->rx_sop, since that
+		 * refers to an entire "DMA packet" not just emptying the
+		 * current fifo.  Most segments need multiple usb packets.
+		 */
+		if (channel->status == MUSB_DMA_STATUS_BUSY)
+			udelay(50);
+
+		/* scan the current list, reporting any data that was
+		 * transferred and acking any IRQ
+		 */
+		cppi_rx_scan(controller, cppi_ch->index);
+
+		/* clobber the existing state once it's idle
+		 *
+		 * NOTE:  arguably, we should also wait for all the other
+		 * RX channels to quiesce (how??) and then temporarily
+		 * disable RXCPPI_CTRL_REG ... but it seems that we can
+		 * rely on the controller restarting from state ram, with
+		 * only RXCPPI_BUFCNT state being bogus.  BUFCNT will
+		 * correct itself after the next DMA transfer though.
+		 *
+		 * REVISIT does using rndis mode change that?
+		 */
+		cppi_reset_rx(cppi_ch->state_ram);
+
+		/* next DMA request _should_ load cppi head ptr */
+
+		/* ... we don't "free" that list, only mutate it in place.  */
+		cppi_dump_rx(5, cppi_ch, " (done abort)");
+
+		/* clean up previously pending bds */
+		cppi_bd_free(cppi_ch, cppi_ch->last_processed);
+		cppi_ch->last_processed = NULL;
+
+		while (queue) {
+			struct cppi_descriptor	*tmp = queue->next;
+
+			cppi_bd_free(cppi_ch, queue);
+			queue = tmp;
+		}
+	}
+
+	channel->status = MUSB_DMA_STATUS_FREE;
+	cppi_ch->buf_dma = 0;
+	cppi_ch->offset = 0;
+	cppi_ch->buf_len = 0;
+	cppi_ch->maxpacket = 0;
+	return 0;
+}
+
+/* TBD Queries:
+ *
+ * Power Management ... probably turn off cppi during suspend, restart;
+ * check state ram?  Clocking is presumably shared with usb core.
+ */