include/asm/dma.h

/* $Id: dma.h,v 1.7 1992/12/14 00:29:34 root Exp root $
 * linux/include/asm/dma.h: Defines for using and allocating dma channels.
 * Written by Hennus Bergman, 1992.
 * High DMA channel support & info by Hannu Savolainen
 * and John Boyd, Nov. 1992.
 */

#ifndef _ASM_DMA_H
#define _ASM_DMA_H

#include <asm/io.h>        /* need byte IO */

#ifdef HAVE_REALLY_SLOW_DMA_CONTROLLER
#define outb    outb_p
#endif

/*
 * NOTES about DMA transfers:
 *
 *  controller 1: channels 0-3, byte operations, ports 00-1F
 *  controller 2: channels 4-7, word operations, ports C0-DF
 *
 *  - ALL registers are 8 bits only, regardless of transfer size
 *  - channel 4 is not used - cascades 1 into 2.
 *  - channels 0-3 are byte - addresses/counts are for physical bytes
 *  - channels 5-7 are word - addresses/counts are for physical words
 *  - transfers must not cross physical 64K (0-3) or 128K (5-7) boundaries
 *  - transfer count loaded to registers is 1 less than actual count
 *  - controller 2 offsets are all even (2x offsets for controller 1)
 *  - page registers for 5-7 don't use data bit 0, represent 128K pages
 *  - page registers for 0-3 use bit 0, represent 64K pages
 *
 * DMA transfers are limited to the lower 16MB of _physical_ memory.  
 * Note that addresses loaded into registers must be _physical_ addresses,
 * not logical addresses (which may differ if paging is active).
 *
 *  Address mapping for channels 0-3:
 *
 *   A23 ... A16 A15 ... A8  A7 ... A0    (Physical addresses)
 *    |  ...  |   |  ... |   |  ... |
 *    |  ...  |   |  ... |   |  ... |
 *    |  ...  |   |  ... |   |  ... |
 *   P7  ...  P0  A7 ... A0  A7 ... A0   
 * |    Page    | Addr MSB | Addr LSB |   (DMA registers)
 *
 *  Address mapping for channels 5-7:
 *
 *   A23 ... A17 A16 A15 ... A9 A8 A7 ... A1 A0    (Physical addresses)
 *    |  ...  |   \   \   ... \  \  \  ... \  \
 *    |  ...  |    \   \   ... \  \  \  ... \  (not used)
 *    |  ...  |     \   \   ... \  \  \  ... \
 *   P7  ...  P1 (0) A7 A6  ... A0 A7 A6 ... A0   
 * |      Page      |  Addr MSB   |  Addr LSB  |   (DMA registers)
 *
 * Again, channels 5-7 transfer _physical_ words (16 bits), so addresses
 * and counts _must_ be word-aligned (the lowest address bit is _ignored_ at
 * the hardware level, so odd-byte transfers aren't possible).
 *
 * Transfer count (_not # bytes_) is limited to 64K, represented as actual
 * count - 1 : 64K => 0xFFFF, 1 => 0x0000.  Thus, count is always 1 or more,
 * and up to 128K bytes may be transferred on channels 5-7 in one operation.
 *
 */

#define MAX_DMA_CHANNELS    8

/* 8237 DMA controllers */
#define IO_DMA1_BASE    0x00    /* 8 bit slave DMA, channels 0..3 */
#define IO_DMA2_BASE    0xC0    /* 16 bit master DMA, ch 4(=slave input)..7 */

/* DMA controller registers */
#define DMA1_CMD_REG        0x08    /* command register (w) */
#define DMA1_STAT_REG        0x08    /* status register (r) */
#define DMA1_REQ_REG            0x09    /* request register (w) */
#define DMA1_MASK_REG        0x0A    /* single-channel mask (w) */
#define DMA1_MODE_REG        0x0B    /* mode register (w) */
#define DMA1_CLEAR_FF_REG    0x0C    /* clear pointer flip-flop (w) */
#define DMA1_TEMP_REG           0x0D    /* Temporary Register (r) */
#define DMA1_RESET_REG        0x0D    /* Master Clear (w) */
#define DMA1_CLR_MASK_REG       0x0E    /* Clear Mask */
#define DMA1_MASK_ALL_REG       0x0F    /* all-channels mask (w) */

#define DMA2_CMD_REG        0xD0    /* command register (w) */
#define DMA2_STAT_REG        0xD0    /* status register (r) */
#define DMA2_REQ_REG            0xD2    /* request register (w) */
#define DMA2_MASK_REG        0xD4    /* single-channel mask (w) */
#define DMA2_MODE_REG        0xD6    /* mode register (w) */
#define DMA2_CLEAR_FF_REG    0xD8    /* clear pointer flip-flop (w) */
#define DMA2_TEMP_REG           0xDA    /* Temporary Register (r) */
#define DMA2_RESET_REG        0xDA    /* Master Clear (w) */
#define DMA2_CLR_MASK_REG       0xDC    /* Clear Mask */
#define DMA2_MASK_ALL_REG       0xDE    /* all-channels mask (w) */

#define DMA_ADDR_0              0x00    /* DMA address registers */
#define DMA_ADDR_1              0x02
#define DMA_ADDR_2              0x04
#define DMA_ADDR_3              0x06
#define DMA_ADDR_4              0xC0
#define DMA_ADDR_5              0xC4
#define DMA_ADDR_6              0xC8
#define DMA_ADDR_7              0xCC

#define DMA_CNT_0               0x01    /* DMA count registers */
#define DMA_CNT_1               0x03
#define DMA_CNT_2               0x05
#define DMA_CNT_3               0x07
#define DMA_CNT_4               0xC2
#define DMA_CNT_5               0xC6
#define DMA_CNT_6               0xCA
#define DMA_CNT_7               0xCE

#define DMA_PAGE_0              0x87    /* DMA page registers */
#define DMA_PAGE_1              0x83
#define DMA_PAGE_2              0x81
#define DMA_PAGE_3              0x82
#define DMA_PAGE_5              0x8B
#define DMA_PAGE_6              0x89
#define DMA_PAGE_7              0x8A

#define DMA_MODE_READ    0x44    /* I/O to memory, no autoinit, increment, single mode */
#define DMA_MODE_WRITE    0x48    /* memory to I/O, no autoinit, increment, single mode */
#define DMA_MODE_CASCADE 0xC0   /* pass thru DREQ->HRQ, DACK<-HLDA only */

/* enable/disable a specific DMA channel */
//启用指定的DMA通道，实际上就是向指定的端口写命令字
static __inline__ void enable_dma(unsigned int dmanr)
{
    if (dmanr<=3)
        outb(dmanr,  DMA1_MASK_REG);
    else
        outb(dmanr & 3,  DMA2_MASK_REG);
}
//禁止指定的DMA通道，实际上就是向指定的端口写命令字
static __inline__ void disable_dma(unsigned int dmanr)
{
    if (dmanr<=3)
        outb(dmanr | 4,  DMA1_MASK_REG);
    else
        outb((dmanr & 3) | 4,  DMA2_MASK_REG);
}

/* Clear the 'DMA Pointer Flip Flop'.
 * Write 0 for LSB/MSB, 1 for MSB/LSB access.
 * Use this once to initialize the FF to a known state.
 * After that, keep track of it. :-)
 * --- In order to do that, the DMA routines below should ---
 * --- only be used while interrupts are disabled! ---
 */
 //初始化Flip Flop
static __inline__ void clear_dma_ff(unsigned int dmanr)
{
    if (dmanr<=3)
        outb(0,  DMA1_CLEAR_FF_REG);
    else
        outb(0,  DMA2_CLEAR_FF_REG);
}

/* set mode (above) for a specific DMA channel */
//为指定的DMA通道设置模式
static __inline__ void set_dma_mode(unsigned int dmanr, char mode)
{
    if (dmanr<=3)
        outb(mode | dmanr,  DMA1_MODE_REG);
    else
        outb(mode | (dmanr&3),  DMA2_MODE_REG);
}

/* Set only the page register bits of the transfer address.
 * This is used for successive transfers when we know the contents of
 * the lower 16 bits of the DMA current address register, but a 64k boundary
 * may have been crossed.
 */
static __inline__ void set_dma_page(unsigned int dmanr, char pagenr)
{
    switch(dmanr) {
        case 0:
            outb(pagenr, DMA_PAGE_0);
            break;
        case 1:
            outb(pagenr, DMA_PAGE_1);
            break;
        case 2:
            outb(pagenr, DMA_PAGE_2);
            break;
        case 3:
            outb(pagenr, DMA_PAGE_3);
            break;
        case 5:
            outb(pagenr & 0xfe, DMA_PAGE_5);
            break;
        case 6:
            outb(pagenr & 0xfe, DMA_PAGE_6);
            break;
        case 7:
            outb(pagenr & 0xfe, DMA_PAGE_7);
            break;
    }
}

/* Set transfer address & page bits for specific DMA channel.
 * Assumes dma flipflop is clear.
 */
 //设置dma的传输地址
static __inline__ void set_dma_addr(unsigned int dmanr, unsigned int a)
{
    set_dma_page(dmanr, a>>16);
    if (dmanr <= 3)  {
        outb( a & 0xff, ((dmanr&3)<<1) + IO_DMA1_BASE );
            outb( (a>>8) & 0xff, ((dmanr&3)<<1) + IO_DMA1_BASE );
    }  else  {
        outb( (a>>1) & 0xff, ((dmanr&3)<<2) + IO_DMA2_BASE );
        outb( (a>>9) & 0xff, ((dmanr&3)<<2) + IO_DMA2_BASE );
    }
}

/* Set transfer size (max 64k for DMA1..3, 128k for DMA5..7) for
 * a specific DMA channel.
 * You must ensure the parameters are valid.
 * NOTE: from a manual: "the number of transfers is one more
 * than the initial word count"! This is taken into account.
 * Assumes dma flip-flop is clear.
 * NOTE 2: "count" represents _bytes_ and must be even for channels 5-7.
 */
 //设置dma的传输长度
static __inline__ void set_dma_count(unsigned int dmanr, unsigned int count)
{
        count--;
    if (dmanr <= 3)  {
        outb( count & 0xff, ((dmanr&3)<<1) + 1 + IO_DMA1_BASE );
        outb( (count>>8) & 0xff, ((dmanr&3)<<1) + 1 + IO_DMA1_BASE );
        } else {
        outb( (count>>1) & 0xff, ((dmanr&3)<<2) + 2 + IO_DMA2_BASE );
        outb( (count>>9) & 0xff, ((dmanr&3)<<2) + 2 + IO_DMA2_BASE );
        }
}

/* Get DMA residue count. After a DMA transfer, this
 * should return zero. Reading this while a DMA transfer is
 * still in progress will return unpredictable results.
 * If called before the channel has been used, it may return 1.
 * Otherwise, it returns the number of _bytes_ left to transfer.
 *
 * Assumes DMA flip-flop is clear.
 */
 //获取dma传输剩余长度
static __inline__ int get_dma_residue(unsigned int dmanr)
{
    unsigned int io_port = (dmanr<=3)? ((dmanr&3)<<1) + 1 + IO_DMA1_BASE
                     : ((dmanr&3)<<2) + 2 + IO_DMA2_BASE;

/* using short to get 16-bit wrap around */
    unsigned short count;

count = 1 + inb(io_port);
    count += inb(io_port) << 8;
    
    return (dmanr<=3)? count : (count<<1);
}

/* These are in kernel/dma.c: */
extern int request_dma(unsigned int dmanr);    /* reserve a DMA channel */
extern void free_dma(unsigned int dmanr);    /* release it again */

#endif /* _ASM_DMA_H */