include/asm-x86/dma.h - linux - Git at Google

 /*
  * 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_X86__DMA_H
 #define ASM_X86__DMA_H

 #include <linux/spinlock.h>	/* And spinlocks */
 #include <asm/io.h>		/* need byte IO */
 #include <linux/delay.h>

 #ifdef HAVE_REALLY_SLOW_DMA_CONTROLLER
 #define dma_outb	outb_p
 #else
 #define dma_outb	outb
 #endif

 #define dma_inb		inb

 /*
  * 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

 #ifdef CONFIG_X86_32

 /* The maximum address that we can perform a DMA transfer to on this platform */
 #define MAX_DMA_ADDRESS      (PAGE_OFFSET + 0x1000000)

 #else

 /* 16MB ISA DMA zone */
 #define MAX_DMA_PFN   ((16 * 1024 * 1024) >> PAGE_SHIFT)

 /* 4GB broken PCI/AGP hardware bus master zone */
 #define MAX_DMA32_PFN ((4UL * 1024 * 1024 * 1024) >> PAGE_SHIFT)

 /* Compat define for old dma zone */
 #define MAX_DMA_ADDRESS ((unsigned long)__va(MAX_DMA_PFN << PAGE_SHIFT))

 #endif

 /* 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

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

 #define DMA_AUTOINIT		0x10


 extern spinlock_t  dma_spin_lock;

 static inline unsigned long claim_dma_lock(void)
 {
 	unsigned long flags;
 	spin_lock_irqsave(&dma_spin_lock, flags);
 	return flags;
 }

 static inline void release_dma_lock(unsigned long flags)
 {
 	spin_unlock_irqrestore(&dma_spin_lock, flags);
 }

 /* enable/disable a specific DMA channel */
 static inline void enable_dma(unsigned int dmanr)
 {
 	if (dmanr <= 3)
 		dma_outb(dmanr, DMA1_MASK_REG);
 	else
 		dma_outb(dmanr & 3, DMA2_MASK_REG);
 }

 static inline void disable_dma(unsigned int dmanr)
 {
 	if (dmanr <= 3)
 		dma_outb(dmanr | 4, DMA1_MASK_REG);
 	else
 		dma_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 holding the DMA lock ! ---
  */
 static inline void clear_dma_ff(unsigned int dmanr)
 {
 	if (dmanr <= 3)
 		dma_outb(0, DMA1_CLEAR_FF_REG);
 	else
 		dma_outb(0, DMA2_CLEAR_FF_REG);
 }

 /* set mode (above) for a specific DMA channel */
 static inline void set_dma_mode(unsigned int dmanr, char mode)
 {
 	if (dmanr <= 3)
 		dma_outb(mode | dmanr, DMA1_MODE_REG);
 	else
 		dma_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:
 		dma_outb(pagenr, DMA_PAGE_0);
 		break;
 	case 1:
 		dma_outb(pagenr, DMA_PAGE_1);
 		break;
 	case 2:
 		dma_outb(pagenr, DMA_PAGE_2);
 		break;
 	case 3:
 		dma_outb(pagenr, DMA_PAGE_3);
 		break;
 	case 5:
 		dma_outb(pagenr & 0xfe, DMA_PAGE_5);
 		break;
 	case 6:
 		dma_outb(pagenr & 0xfe, DMA_PAGE_6);
 		break;
 	case 7:
 		dma_outb(pagenr & 0xfe, DMA_PAGE_7);
 		break;
 	}
 }


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


 /* Set transfer size (max 64k for DMA0..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.
  */
 static inline void set_dma_count(unsigned int dmanr, unsigned int count)
 {
 	count--;
 	if (dmanr <= 3)  {
 		dma_outb(count & 0xff, ((dmanr & 3) << 1) + 1 + IO_DMA1_BASE);
 		dma_outb((count >> 8) & 0xff,
 			 ((dmanr & 3) << 1) + 1 + IO_DMA1_BASE);
 	} else {
 		dma_outb((count >> 1) & 0xff,
 			 ((dmanr & 3) << 2) + 2 + IO_DMA2_BASE);
 		dma_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.
  */
 static inline int get_dma_residue(unsigned int dmanr)
 {
 	unsigned int io_port;
 	/* using short to get 16-bit wrap around */
 	unsigned short count;

 	io_port = (dmanr <= 3) ? ((dmanr & 3) << 1) + 1 + IO_DMA1_BASE
 		: ((dmanr & 3) << 2) + 2 + IO_DMA2_BASE;

 	count = 1 + dma_inb(io_port);
 	count += dma_inb(io_port) << 8;

 	return (dmanr <= 3) ? count : (count << 1);
 }


 /* These are in kernel/dma.c: */
 extern int request_dma(unsigned int dmanr, const char *device_id);
 extern void free_dma(unsigned int dmanr);

 /* From PCI */

 #ifdef CONFIG_PCI
 extern int isa_dma_bridge_buggy;
 #else
 #define isa_dma_bridge_buggy	(0)
 #endif

 #endif /* ASM_X86__DMA_H */
	/*
	* 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_X86__DMA_H
	#define ASM_X86__DMA_H

	#include <linux/spinlock.h> /* And spinlocks */
	#include <asm/io.h> /* need byte IO */
	#include <linux/delay.h>

	#ifdef HAVE_REALLY_SLOW_DMA_CONTROLLER
	#define dma_outb outb_p
	#else
	#define dma_outb outb
	#endif

	#define dma_inb inb

	/*
	* 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

	#ifdef CONFIG_X86_32

	/* The maximum address that we can perform a DMA transfer to on this platform */
	#define MAX_DMA_ADDRESS (PAGE_OFFSET + 0x1000000)

	#else

	/* 16MB ISA DMA zone */
	#define MAX_DMA_PFN ((16 * 1024 * 1024) >> PAGE_SHIFT)

	/* 4GB broken PCI/AGP hardware bus master zone */
	#define MAX_DMA32_PFN ((4UL * 1024 * 1024 * 1024) >> PAGE_SHIFT)

	/* Compat define for old dma zone */
	#define MAX_DMA_ADDRESS ((unsigned long)__va(MAX_DMA_PFN << PAGE_SHIFT))

	#endif

	/* 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

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

	#define DMA_AUTOINIT 0x10


	extern spinlock_t dma_spin_lock;

	static inline unsigned long claim_dma_lock(void)
	{
	unsigned long flags;
	spin_lock_irqsave(&dma_spin_lock, flags);
	return flags;
	}

	static inline void release_dma_lock(unsigned long flags)
	{
	spin_unlock_irqrestore(&dma_spin_lock, flags);
	}

	/* enable/disable a specific DMA channel */
	static inline void enable_dma(unsigned int dmanr)
	{
	if (dmanr <= 3)
	dma_outb(dmanr, DMA1_MASK_REG);
	else
	dma_outb(dmanr & 3, DMA2_MASK_REG);
	}

	static inline void disable_dma(unsigned int dmanr)
	{
	if (dmanr <= 3)
	dma_outb(dmanr \| 4, DMA1_MASK_REG);
	else
	dma_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 holding the DMA lock ! ---
	*/
	static inline void clear_dma_ff(unsigned int dmanr)
	{
	if (dmanr <= 3)
	dma_outb(0, DMA1_CLEAR_FF_REG);
	else
	dma_outb(0, DMA2_CLEAR_FF_REG);
	}

	/* set mode (above) for a specific DMA channel */
	static inline void set_dma_mode(unsigned int dmanr, char mode)
	{
	if (dmanr <= 3)
	dma_outb(mode \| dmanr, DMA1_MODE_REG);
	else
	dma_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:
	dma_outb(pagenr, DMA_PAGE_0);
	break;
	case 1:
	dma_outb(pagenr, DMA_PAGE_1);
	break;
	case 2:
	dma_outb(pagenr, DMA_PAGE_2);
	break;
	case 3:
	dma_outb(pagenr, DMA_PAGE_3);
	break;
	case 5:
	dma_outb(pagenr & 0xfe, DMA_PAGE_5);
	break;
	case 6:
	dma_outb(pagenr & 0xfe, DMA_PAGE_6);
	break;
	case 7:
	dma_outb(pagenr & 0xfe, DMA_PAGE_7);
	break;
	}
	}


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


	/* Set transfer size (max 64k for DMA0..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.
	*/
	static inline void set_dma_count(unsigned int dmanr, unsigned int count)
	{
	count--;
	if (dmanr <= 3) {
	dma_outb(count & 0xff, ((dmanr & 3) << 1) + 1 + IO_DMA1_BASE);
	dma_outb((count >> 8) & 0xff,
	((dmanr & 3) << 1) + 1 + IO_DMA1_BASE);
	} else {
	dma_outb((count >> 1) & 0xff,
	((dmanr & 3) << 2) + 2 + IO_DMA2_BASE);
	dma_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.
	*/
	static inline int get_dma_residue(unsigned int dmanr)
	{
	unsigned int io_port;
	/* using short to get 16-bit wrap around */
	unsigned short count;

	io_port = (dmanr <= 3) ? ((dmanr & 3) << 1) + 1 + IO_DMA1_BASE
	: ((dmanr & 3) << 2) + 2 + IO_DMA2_BASE;

	count = 1 + dma_inb(io_port);
	count += dma_inb(io_port) << 8;

	return (dmanr <= 3) ? count : (count << 1);
	}


	/* These are in kernel/dma.c: */
	extern int request_dma(unsigned int dmanr, const char *device_id);
	extern void free_dma(unsigned int dmanr);

	/* From PCI */

	#ifdef CONFIG_PCI
	extern int isa_dma_bridge_buggy;
	#else
	#define isa_dma_bridge_buggy (0)
	#endif

	#endif /* ASM_X86__DMA_H */