arch/mips/include/asm/dma.h

Source file repositories/reference/linux-study-clean/arch/mips/include/asm/dma.h

File Facts

System
Linux kernel
Corpus path
arch/mips/include/asm/dma.h
Extension
.h
Size
10047 bytes
Lines
311
Domain
Architecture Layer
Bucket
arch/mips
Inferred role
Architecture Layer: implementation source
Status
source implementation candidate

Why This File Exists

CPU and platform-specific kernel glue: boot entry, traps, syscall entry, interrupts, page tables, context switch, and low-level barriers.

Dependency Surface

Detected Declarations

Annotated Snippet

#ifndef _ASM_DMA_H
#define _ASM_DMA_H

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

#ifndef CONFIG_GENERIC_ISA_DMA_SUPPORT_BROKEN
#define MAX_DMA_CHANNELS	8
#endif

/*
 * The maximum address in KSEG0 that we can perform a DMA transfer to on this
 * platform.  This describes only the PC style part of the DMA logic like on
 * Deskstations or Acer PICA but not the much more versatile DMA logic used
 * for the local devices on Acer PICA or Magnums.
 */
#if defined(CONFIG_SGI_IP22) || defined(CONFIG_SGI_IP28)
/* don't care; ISA bus master won't work, ISA slave DMA supports 32bit addr */
#define MAX_DMA_ADDRESS		PAGE_OFFSET
#else
#define MAX_DMA_ADDRESS		(PAGE_OFFSET + 0x01000000)
#endif
#define MAX_DMA_PFN		PFN_DOWN(virt_to_phys((void *)MAX_DMA_ADDRESS))

#ifndef MAX_DMA32_PFN
#define MAX_DMA32_PFN		(1UL << (32 - 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 */

Annotation

Implementation Notes