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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150// 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_CHANNELSstatic 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;}#elsestatic 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);