1 files changed, 149 insertions, 0 deletions
diff --git a/kernel/dma.c b/kernel/dma.c
new file mode 100644
index 000000000..40f152936
--- /dev/null
+++ b/kernel/dma.c
@@ -0,0 +1,149 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * linux/kernel/dma.c: A DMA channel allocator. Inspired by linux/kernel/irq.c.
+ *
+ * Written by Hennus Bergman, 1992.
+ *
+ * 1994/12/26: Changes by Alex Nash to fix a minor bug in /proc/dma.
+ *   In the previous version the reported device could end up being wrong,
+ *   if a device requested a DMA channel that was already in use.
+ *   [It also happened to remove the sizeof(char *) == sizeof(int)
+ *   assumption introduced because of those /proc/dma patches. -- Hennus]
+ */
+#include <linux/export.h>
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/spinlock.h>
+#include <linux/string.h>
+#include <linux/seq_file.h>
+#include <linux/proc_fs.h>
+#include <linux/init.h>
+#include <asm/dma.h>
+
+
+
+/* A note on resource allocation:
+ *
+ * All drivers needing DMA channels, should allocate and release them
+ * through the public routines `request_dma()' and `free_dma()'.
+ *
+ * In order to avoid problems, all processes should allocate resources in
+ * the same sequence and release them in the reverse order.
+ *
+ * So, when allocating DMAs and IRQs, first allocate the IRQ, then the DMA.
+ * When releasing them, first release the DMA, then release the IRQ.
+ * If you don't, you may cause allocation requests to fail unnecessarily.
+ * This doesn't really matter now, but it will once we get real semaphores
+ * in the kernel.
+ */
+
+
+DEFINE_SPINLOCK(dma_spin_lock);
+
+/*
+ *	If our port doesn't define this it has no PC like DMA
+ */
+
+#ifdef MAX_DMA_CHANNELS
+
+
+/* Channel n is busy iff dma_chan_busy[n].lock != 0.
+ * DMA0 used to be reserved for DRAM refresh, but apparently not any more...
+ * DMA4 is reserved for cascading.
+ */
+
+struct dma_chan {
+	int  lock;
+	const char *device_id;
+};
+
+static struct dma_chan dma_chan_busy[MAX_DMA_CHANNELS] = {
+	[4] = { 1, "cascade" },
+};
+
+
+/**
+ * request_dma - request and reserve a system DMA channel
+ * @dmanr: DMA channel number
+ * @device_id: reserving device ID string, used in /proc/dma
+ */
+int request_dma(unsigned int dmanr, const char * device_id)
+{
+	if (dmanr >= MAX_DMA_CHANNELS)
+		return -EINVAL;
+
+	if (xchg(&dma_chan_busy[dmanr].lock, 1) != 0)
+		return -EBUSY;
+
+	dma_chan_busy[dmanr].device_id = device_id;
+
+	/* old flag was 0, now contains 1 to indicate busy */
+	return 0;
+} /* request_dma */
+
+/**
+ * free_dma - free a reserved system DMA channel
+ * @dmanr: DMA channel number
+ */
+void free_dma(unsigned int dmanr)
+{
+	if (dmanr >= MAX_DMA_CHANNELS) {
+		printk(KERN_WARNING "Trying to free DMA%d\n", dmanr);
+		return;
+	}
+
+	if (xchg(&dma_chan_busy[dmanr].lock, 0) == 0) {
+		printk(KERN_WARNING "Trying to free free DMA%d\n", dmanr);
+		return;
+	}
+
+} /* free_dma */
+
+#else
+
+int request_dma(unsigned int dmanr, const char *device_id)
+{
+	return -EINVAL;
+}
+
+void free_dma(unsigned int dmanr)
+{
+}
+
+#endif
+
+#ifdef CONFIG_PROC_FS
+
+#ifdef MAX_DMA_CHANNELS
+static int proc_dma_show(struct seq_file *m, void *v)
+{
+	int i;
+
+	for (i = 0 ; i < MAX_DMA_CHANNELS ; i++) {
+		if (dma_chan_busy[i].lock) {
+			seq_printf(m, "%2d: %s\n", i,
+				   dma_chan_busy[i].device_id);
+		}
+	}
+	return 0;
+}
+#else
+static int proc_dma_show(struct seq_file *m, void *v)
+{
+	seq_puts(m, "No DMA\n");
+	return 0;
+}
+#endif /* MAX_DMA_CHANNELS */
+
+static int __init proc_dma_init(void)
+{
+	proc_create_single("dma", 0, NULL, proc_dma_show);
+	return 0;
+}
+
+__initcall(proc_dma_init);
+#endif
+
+EXPORT_SYMBOL(request_dma);
+EXPORT_SYMBOL(free_dma);
+EXPORT_SYMBOL(dma_spin_lock);