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Annotation of Gnu-Mach/linux/src/kernel/dma.c, revision 1.1

1.1     ! root        1: /* $Id: dma.c,v 1.1 1999/04/26 05:58:29 tb Exp $
        !             2:  * linux/kernel/dma.c: A DMA channel allocator. Inspired by linux/kernel/irq.c.
        !             3:  *
        !             4:  * Written by Hennus Bergman, 1992.
        !             5:  *
        !             6:  * 1994/12/26: Changes by Alex Nash to fix a minor bug in /proc/dma.
        !             7:  *   In the previous version the reported device could end up being wrong,
        !             8:  *   if a device requested a DMA channel that was already in use.
        !             9:  *   [It also happened to remove the sizeof(char *) == sizeof(int)
        !            10:  *   assumption introduced because of those /proc/dma patches. -- Hennus]
        !            11:  */
        !            12: 
        !            13: #include <linux/kernel.h>
        !            14: #include <linux/errno.h>
        !            15: #include <asm/dma.h>
        !            16: #include <asm/system.h>
        !            17: 
        !            18: 
        !            19: /* A note on resource allocation:
        !            20:  *
        !            21:  * All drivers needing DMA channels, should allocate and release them
        !            22:  * through the public routines `request_dma()' and `free_dma()'.
        !            23:  *
        !            24:  * In order to avoid problems, all processes should allocate resources in
        !            25:  * the same sequence and release them in the reverse order.
        !            26:  *
        !            27:  * So, when allocating DMAs and IRQs, first allocate the IRQ, then the DMA.
        !            28:  * When releasing them, first release the DMA, then release the IRQ.
        !            29:  * If you don't, you may cause allocation requests to fail unnecessarily.
        !            30:  * This doesn't really matter now, but it will once we get real semaphores
        !            31:  * in the kernel.
        !            32:  */
        !            33: 
        !            34: 
        !            35: 
        !            36: /* Channel n is busy iff dma_chan_busy[n].lock != 0.
        !            37:  * DMA0 used to be reserved for DRAM refresh, but apparently not any more...
        !            38:  * DMA4 is reserved for cascading.
        !            39:  */
        !            40: 
        !            41: struct dma_chan {
        !            42:        int  lock;
        !            43:        const char *device_id;
        !            44: };
        !            45: 
        !            46: static struct dma_chan dma_chan_busy[MAX_DMA_CHANNELS] = {
        !            47:        { 0, 0 },
        !            48:        { 0, 0 },
        !            49:        { 0, 0 },
        !            50:        { 0, 0 },
        !            51:        { 1, "cascade" },
        !            52:        { 0, 0 },
        !            53:        { 0, 0 },
        !            54:        { 0, 0 }
        !            55: };
        !            56: 
        !            57: int get_dma_list(char *buf)
        !            58: {
        !            59:        int i, len = 0;
        !            60: 
        !            61:        for (i = 0 ; i < MAX_DMA_CHANNELS ; i++) {
        !            62:                if (dma_chan_busy[i].lock) {
        !            63:                    len += sprintf(buf+len, "%2d: %s\n",
        !            64:                                   i,
        !            65:                                   dma_chan_busy[i].device_id);
        !            66:                }
        !            67:        }
        !            68:        return len;
        !            69: } /* get_dma_list */
        !            70: 
        !            71: 
        !            72: int request_dma(unsigned int dmanr, const char * device_id)
        !            73: {
        !            74:        if (dmanr >= MAX_DMA_CHANNELS)
        !            75:                return -EINVAL;
        !            76: 
        !            77:        if (xchg(&dma_chan_busy[dmanr].lock, 1) != 0)
        !            78:                return -EBUSY;
        !            79: 
        !            80:        dma_chan_busy[dmanr].device_id = device_id;
        !            81: 
        !            82:        /* old flag was 0, now contains 1 to indicate busy */
        !            83:        return 0;
        !            84: } /* request_dma */
        !            85: 
        !            86: 
        !            87: void free_dma(unsigned int dmanr)
        !            88: {
        !            89:        if (dmanr >= MAX_DMA_CHANNELS) {
        !            90:                printk("Trying to free DMA%d\n", dmanr);
        !            91:                return;
        !            92:        }
        !            93: 
        !            94:        if (xchg(&dma_chan_busy[dmanr].lock, 0) == 0) {
        !            95:                printk("Trying to free free DMA%d\n", dmanr);
        !            96:                return;
        !            97:        }       
        !            98: 
        !            99: } /* free_dma */

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