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Release 4.15 kernel/dma.c

Directory: kernel
// 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; }

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Linus Torvalds (pre-git)58100.00%5100.00%
Total58100.00%5100.00%

/* 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; } }

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Linus Torvalds (pre-git)5296.30%480.00%
Cory Watson23.70%120.00%
Total54100.00%5100.00%

/* free_dma */ #else
int request_dma(unsigned int dmanr, const char *device_id) { return -EINVAL; }

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Sam Ravnborg18100.00%1100.00%
Total18100.00%1100.00%


void free_dma(unsigned int dmanr) { }

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PersonTokensPropCommitsCommitProp
Sam Ravnborg8100.00%1100.00%
Total8100.00%1100.00%

#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; }

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Russell King63100.00%1100.00%
Total63100.00%1100.00%

#else
static int proc_dma_show(struct seq_file *m, void *v) { seq_puts(m, "No DMA\n"); return 0; }

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Russell King25100.00%1100.00%
Total25100.00%1100.00%

#endif /* MAX_DMA_CHANNELS */
static int proc_dma_open(struct inode *inode, struct file *file) { return single_open(file, proc_dma_show, NULL); }

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PersonTokensPropCommitsCommitProp
Russell King2492.31%150.00%
Linus Torvalds (pre-git)27.69%150.00%
Total26100.00%2100.00%

static const struct file_operations proc_dma_operations = { .open = proc_dma_open, .read = seq_read, .llseek = seq_lseek, .release = single_release, };
static int __init proc_dma_init(void) { proc_create("dma", 0, NULL, &proc_dma_operations); return 0; }

Contributors

PersonTokensPropCommitsCommitProp
Russell King1770.83%133.33%
Linus Torvalds (pre-git)416.67%133.33%
Denis V. Lunev312.50%133.33%
Total24100.00%3100.00%

__initcall(proc_dma_init); #endif EXPORT_SYMBOL(request_dma); EXPORT_SYMBOL(free_dma); EXPORT_SYMBOL(dma_spin_lock);

Overall Contributors

PersonTokensPropCommitsCommitProp
Russell King18143.30%14.55%
Linus Torvalds (pre-git)17241.15%1045.45%
Sam Ravnborg378.85%14.55%
Art Haas81.91%14.55%
Linus Torvalds51.20%14.55%
Thomas Gleixner40.96%14.55%
Denis V. Lunev30.72%14.55%
Randy Dunlap20.48%14.55%
Cory Watson20.48%14.55%
Adrian Bunk10.24%14.55%
Greg Kroah-Hartman10.24%14.55%
Paul Gortmaker10.24%14.55%
Helge Deller10.24%14.55%
Total418100.00%22100.00%
Directory: kernel
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