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dma.c
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dma.c
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// 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);