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diff --git a/arch/m68k/include/asm/mac_psc.h b/arch/m68k/include/asm/mac_psc.h
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+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Apple Peripheral System Controller (PSC)
+ *
+ * The PSC is used on the AV Macs to control IO functions not handled
+ * by the VIAs (Ethernet, DSP, SCC, Sound). This includes nine DMA
+ * channels.
+ *
+ * The first seven DMA channels appear to be "one-shot" and are actually
+ * sets of two channels; one member is active while the other is being
+ * configured, and then you flip the active member and start all over again.
+ * The one-shot channels are grouped together and are:
+ *
+ * 1. SCSI
+ * 2. Ethernet Read
+ * 3. Ethernet Write
+ * 4. Floppy Disk Controller
+ * 5. SCC Channel A Receive
+ * 6. SCC Channel B Receive
+ * 7. SCC Channel A Transmit
+ *
+ * The remaining two channels are handled somewhat differently. They appear
+ * to be closely tied and share one set of registers. They also seem to run
+ * continuously, although how you keep the buffer filled in this scenario is
+ * not understood as there seems to be only one input and one output buffer
+ * pointer.
+ *
+ * Much of this was extrapolated from what was known about the Ethernet
+ * registers and subsequently confirmed using MacsBug (ie by pinging the
+ * machine with easy-to-find patterns and looking for them in the DMA
+ * buffers, or by sending a file over the serial ports and finding the
+ * file in the buffers.)
+ *
+ * 1999-05-25 (jmt)
+ */
+
+#define PSC_BASE (0x50F31000)
+
+/*
+ * The IER/IFR registers work like the VIA, except that it has 4
+ * of them each on different interrupt levels, and each register
+ * set only seems to handle four interrupts instead of seven.
+ *
+ * To access a particular set of registers, add 0xn0 to the base
+ * where n = 3,4,5 or 6.
+ */
+
+#define pIFRbase 0x100
+#define pIERbase 0x104
+
+/*
+ * One-shot DMA control registers
+ */
+
+#define PSC_MYSTERY 0x804
+
+#define PSC_CTL_BASE 0xC00
+
+#define PSC_SCSI_CTL 0xC00
+#define PSC_ENETRD_CTL 0xC10
+#define PSC_ENETWR_CTL 0xC20
+#define PSC_FDC_CTL 0xC30
+#define PSC_SCCA_CTL 0xC40
+#define PSC_SCCB_CTL 0xC50
+#define PSC_SCCATX_CTL 0xC60
+
+/*
+ * DMA channels. Add +0x10 for the second channel in the set.
+ * You're supposed to use one channel while the other runs and
+ * then flip channels and do the whole thing again.
+ */
+
+#define PSC_ADDR_BASE 0x1000
+#define PSC_LEN_BASE 0x1004
+#define PSC_CMD_BASE 0x1008
+
+#define PSC_SET0 0x00
+#define PSC_SET1 0x10
+
+#define PSC_SCSI_ADDR 0x1000 /* confirmed */
+#define PSC_SCSI_LEN 0x1004 /* confirmed */
+#define PSC_SCSI_CMD 0x1008 /* confirmed */
+#define PSC_ENETRD_ADDR 0x1020 /* confirmed */
+#define PSC_ENETRD_LEN 0x1024 /* confirmed */
+#define PSC_ENETRD_CMD 0x1028 /* confirmed */
+#define PSC_ENETWR_ADDR 0x1040 /* confirmed */
+#define PSC_ENETWR_LEN 0x1044 /* confirmed */
+#define PSC_ENETWR_CMD 0x1048 /* confirmed */
+#define PSC_FDC_ADDR 0x1060 /* strongly suspected */
+#define PSC_FDC_LEN 0x1064 /* strongly suspected */
+#define PSC_FDC_CMD 0x1068 /* strongly suspected */
+#define PSC_SCCA_ADDR 0x1080 /* confirmed */
+#define PSC_SCCA_LEN 0x1084 /* confirmed */
+#define PSC_SCCA_CMD 0x1088 /* confirmed */
+#define PSC_SCCB_ADDR 0x10A0 /* confirmed */
+#define PSC_SCCB_LEN 0x10A4 /* confirmed */
+#define PSC_SCCB_CMD 0x10A8 /* confirmed */
+#define PSC_SCCATX_ADDR 0x10C0 /* confirmed */
+#define PSC_SCCATX_LEN 0x10C4 /* confirmed */
+#define PSC_SCCATX_CMD 0x10C8 /* confirmed */
+
+/*
+ * Free-running DMA registers. The only part known for sure are the bits in
+ * the control register, the buffer addresses and the buffer length. Everything
+ * else is anybody's guess.
+ *
+ * These registers seem to be mirrored every thirty-two bytes up until offset
+ * 0x300. It's safe to assume then that a new set of registers starts there.
+ */
+
+#define PSC_SND_CTL 0x200 /*
+ * [ 16-bit ]
+ * Sound (Singer?) control register.
+ *
+ * bit 0 : ????
+ * bit 1 : ????
+ * bit 2 : Set to one to enable sound
+ * output. Possibly a mute flag.
+ * bit 3 : ????
+ * bit 4 : ????
+ * bit 5 : ????
+ * bit 6 : Set to one to enable pass-thru
+ * audio. In this mode the audio data
+ * seems to appear in both the input
+ * buffer and the output buffer.
+ * bit 7 : Set to one to activate the
+ * sound input DMA or zero to
+ * disable it.
+ * bit 8 : Set to one to activate the
+ * sound output DMA or zero to
+ * disable it.
+ * bit 9 : \
+ * bit 11 : |
+ * These two bits control the sample
+ * rate. Usually set to binary 10 and
+ * MacOS 8.0 says I'm at 48 KHz. Using
+ * a binary value of 01 makes things
+ * sound about 1/2 speed (24 KHz?) and
+ * binary 00 is slower still (22 KHz?)
+ *
+ * Setting this to 0x0000 is a good way to
+ * kill all DMA at boot time so that the
+ * PSC won't overwrite the kernel image
+ * with sound data.
+ */
+
+/*
+ * 0x0202 - 0x0203 is unused. Writing there
+ * seems to clobber the control register.
+ */
+
+#define PSC_SND_SOURCE 0x204 /*
+ * [ 32-bit ]
+ * Controls input source and volume:
+ *
+ * bits 12-15 : input source volume, 0 - F
+ * bits 16-19 : unknown, always 0x5
+ * bits 20-23 : input source selection:
+ * 0x3 = CD Audio
+ * 0x4 = External Audio
+ *
+ * The volume is definitely not the general
+ * output volume as it doesn't affect the
+ * alert sound volume.
+ */
+#define PSC_SND_STATUS1 0x208 /*
+ * [ 32-bit ]
+ * Appears to be a read-only status register.
+ * The usual value is 0x00400002.
+ */
+#define PSC_SND_HUH3 0x20C /*
+ * [ 16-bit ]
+ * Unknown 16-bit value, always 0x0000.
+ */
+#define PSC_SND_BITS2GO 0x20E /*
+ * [ 16-bit ]
+ * Counts down to zero from some constant
+ * value. The value appears to be the
+ * number of _bits_ remaining before the
+ * buffer is full, which would make sense
+ * since Apple's docs say the sound DMA
+ * channels are 1 bit wide.
+ */
+#define PSC_SND_INADDR 0x210 /*
+ * [ 32-bit ]
+ * Address of the sound input DMA buffer
+ */
+#define PSC_SND_OUTADDR 0x214 /*
+ * [ 32-bit ]
+ * Address of the sound output DMA buffer
+ */
+#define PSC_SND_LEN 0x218 /*
+ * [ 16-bit ]
+ * Length of both buffers in eight-byte units.
+ */
+#define PSC_SND_HUH4 0x21A /*
+ * [ 16-bit ]
+ * Unknown, always 0x0000.
+ */
+#define PSC_SND_STATUS2 0x21C /*
+ * [ 16-bit ]
+ * Appears to e a read-only status register.
+ * The usual value is 0x0200.
+ */
+#define PSC_SND_HUH5 0x21E /*
+ * [ 16-bit ]
+ * Unknown, always 0x0000.
+ */
+
+#ifndef __ASSEMBLY__
+
+extern volatile __u8 *psc;
+
+extern void psc_register_interrupts(void);
+extern void psc_irq_enable(int);
+extern void psc_irq_disable(int);
+
+/*
+ * Access functions
+ */
+
+static inline void psc_write_byte(int offset, __u8 data)
+{
+ *((volatile __u8 *)(psc + offset)) = data;
+}
+
+static inline void psc_write_word(int offset, __u16 data)
+{
+ *((volatile __u16 *)(psc + offset)) = data;
+}
+
+static inline void psc_write_long(int offset, __u32 data)
+{
+ *((volatile __u32 *)(psc + offset)) = data;
+}
+
+static inline u8 psc_read_byte(int offset)
+{
+ return *((volatile __u8 *)(psc + offset));
+}
+
+static inline u16 psc_read_word(int offset)
+{
+ return *((volatile __u16 *)(psc + offset));
+}
+
+static inline u32 psc_read_long(int offset)
+{
+ return *((volatile __u32 *)(psc + offset));
+}
+
+#endif /* __ASSEMBLY__ */