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