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

1.1     ! root        1: /* $Id: dma.c,v 1.1 1999/04/26 05:49:35 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: #define MACH_INCLUDE
        !            14: #include <linux/kernel.h>
        !            15: #include <linux/errno.h>
        !            16: #include <asm/dma.h>
        !            17: #include <asm/system.h>
        !            18: 
        !            19: 
        !            20: /* A note on resource allocation:
        !            21:  *
        !            22:  * All drivers needing DMA channels, should allocate and release them
        !            23:  * through the public routines `request_dma()' and `free_dma()'.
        !            24:  *
        !            25:  * In order to avoid problems, all processes should allocate resources in
        !            26:  * the same sequence and release them in the reverse order.
        !            27:  *
        !            28:  * So, when allocating DMAs and IRQs, first allocate the IRQ, then the DMA.
        !            29:  * When releasing them, first release the DMA, then release the IRQ.
        !            30:  * If you don't, you may cause allocation requests to fail unnecessarily.
        !            31:  * This doesn't really matter now, but it will once we get real semaphores
        !            32:  * in the kernel.
        !            33:  */
        !            34: 
        !            35: 
        !            36: 
        !            37: /* Channel n is busy iff dma_chan_busy[n].lock != 0.
        !            38:  * DMA0 used to be reserved for DRAM refresh, but apparently not any more...
        !            39:  * DMA4 is reserved for cascading.
        !            40:  */
        !            41: 
        !            42: struct dma_chan
        !            43: {
        !            44:   int  lock;
        !            45:   const char *device_id;
        !            46: };
        !            47: 
        !            48: static struct dma_chan dma_chan_busy[MAX_DMA_CHANNELS] =
        !            49: {
        !            50:   { 0, 0 },
        !            51:   { 0, 0 },
        !            52:   { 0, 0 },
        !            53:   { 0, 0 },
        !            54:   { 1, "cascade" },
        !            55:   { 0, 0 },
        !            56:   { 0, 0 },
        !            57:   { 0, 0 }
        !            58: };
        !            59: 
        !            60: #ifndef MACH
        !            61: int
        !            62: get_dma_list (char *buf)
        !            63: {
        !            64:   int i, len = 0;
        !            65:   
        !            66:   for (i = 0 ; i < MAX_DMA_CHANNELS ; i++)
        !            67:     {
        !            68:       if (dma_chan_busy[i].lock)
        !            69:        {
        !            70:          len += linux_sprintf (buf+len, "%2d: %s\n",
        !            71:                                i,
        !            72:                                dma_chan_busy[i].device_id);
        !            73:        }
        !            74:     }
        !            75:   return len;
        !            76: } /* get_dma_list */
        !            77: #endif
        !            78: 
        !            79: int
        !            80: request_dma (unsigned int dmanr, const char *device_id)
        !            81: {
        !            82:   if (dmanr >= MAX_DMA_CHANNELS)
        !            83:     return -LINUX_EINVAL;
        !            84:   
        !            85:   if (xchg (&dma_chan_busy[dmanr].lock, 1) != 0)
        !            86:     return -LINUX_EBUSY;
        !            87:   
        !            88:   dma_chan_busy[dmanr].device_id = device_id;
        !            89:   
        !            90:   /* old flag was 0, now contains 1 to indicate busy */
        !            91:   return 0;
        !            92: } /* request_dma */
        !            93: 
        !            94: 
        !            95: void
        !            96: free_dma (unsigned int dmanr)
        !            97: {
        !            98:   if (dmanr >= MAX_DMA_CHANNELS)
        !            99:     {
        !           100:       printk ("Trying to free DMA%d\n", dmanr);
        !           101:       return;
        !           102:     }
        !           103:   
        !           104:   if (xchg (&dma_chan_busy[dmanr].lock, 0) == 0)
        !           105:     {
        !           106:       printk ("Trying to free free DMA%d\n", dmanr);
        !           107:       return;
        !           108:     }  
        !           109: } /* free_dma */

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