Linux DMA驱动构架分析

在声卡驱动中药使用到dma 的驱动，现在看看在2.6的内核下dma 的驱动架构

/* linux/arch/arm/mach-s3c2440/dma.c
 *
 * Copyright (c) 2006 Simtec Electronics
 *	Ben Dooks <[email protected]>
 *
 * S3C2440 DMA selection
 *
 * http://armlinux.simtec.co.uk/
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
*/

#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/sysdev.h>
#include <linux/serial_core.h>

#include <mach/dma.h>

#include <plat/dma.h>
#include <plat/cpu.h>

#include <plat/regs-serial.h>
#include <mach/regs-gpio.h>
#include <plat/regs-ac97.h>
#include <mach/regs-mem.h>
#include <mach/regs-lcd.h>
#include <mach/regs-sdi.h>
#include <asm/plat-s3c24xx/regs-iis.h>
#include <plat/regs-spi.h>

static struct s3c24xx_dma_map __initdata s3c2440_dma_mappings[] = {
	[DMACH_XD0] = {
		.name		= "xdreq0",
		.channels[0]	= S3C2410_DCON_CH0_XDREQ0 | DMA_CH_VALID,
	},
	[DMACH_XD1] = {
		.name		= "xdreq1",
		.channels[1]	= S3C2410_DCON_CH1_XDREQ1 | DMA_CH_VALID,
	},
	[DMACH_SDI] = {
		.name		= "sdi",
		.channels[0]	= S3C2410_DCON_CH0_SDI | DMA_CH_VALID,
		.channels[1]	= S3C2440_DCON_CH1_SDI | DMA_CH_VALID,
		.channels[2]	= S3C2410_DCON_CH2_SDI | DMA_CH_VALID,
		.channels[3]	= S3C2410_DCON_CH3_SDI | DMA_CH_VALID,
		.hw_addr.to	= S3C2410_PA_IIS + S3C2410_IISFIFO,
		.hw_addr.from	= S3C2410_PA_IIS + S3C2410_IISFIFO,
	},
	[DMACH_SPI0] = {
		.name		= "spi0",
		.channels[1]	= S3C2410_DCON_CH1_SPI | DMA_CH_VALID,
		.hw_addr.to	= S3C2410_PA_SPI + S3C2410_SPTDAT,
		.hw_addr.from	= S3C2410_PA_SPI + S3C2410_SPRDAT,
	},
	[DMACH_SPI1] = {
		.name		= "spi1",
		.channels[3]	= S3C2410_DCON_CH3_SPI | DMA_CH_VALID,
		.hw_addr.to	= S3C2410_PA_SPI + 0x20 + S3C2410_SPTDAT,
		.hw_addr.from	= S3C2410_PA_SPI + 0x20 + S3C2410_SPRDAT,
	},
	[DMACH_UART0] = {
		.name		= "uart0",
		.channels[0]	= S3C2410_DCON_CH0_UART0 | DMA_CH_VALID,
		.hw_addr.to	= S3C2410_PA_UART0 + S3C2410_UTXH,
		.hw_addr.from	= S3C2410_PA_UART0 + S3C2410_URXH,
	},
	[DMACH_UART1] = {
		.name		= "uart1",
		.channels[1]	= S3C2410_DCON_CH1_UART1 | DMA_CH_VALID,
		.hw_addr.to	= S3C2410_PA_UART1 + S3C2410_UTXH,
		.hw_addr.from	= S3C2410_PA_UART1 + S3C2410_URXH,
	},
      	[DMACH_UART2] = {
		.name		= "uart2",
		.channels[3]	= S3C2410_DCON_CH3_UART2 | DMA_CH_VALID,
		.hw_addr.to	= S3C2410_PA_UART2 + S3C2410_UTXH,
		.hw_addr.from	= S3C2410_PA_UART2 + S3C2410_URXH,
	},
	[DMACH_TIMER] = {
		.name		= "timer",
		.channels[0]	= S3C2410_DCON_CH0_TIMER | DMA_CH_VALID,
		.channels[2]	= S3C2410_DCON_CH2_TIMER | DMA_CH_VALID,
		.channels[3]	= S3C2410_DCON_CH3_TIMER | DMA_CH_VALID,
	},
	[DMACH_I2S_IN] = {
		.name		= "i2s-sdi",
		.channels[1]	= S3C2410_DCON_CH1_I2SSDI | DMA_CH_VALID,
		.channels[2]	= S3C2410_DCON_CH2_I2SSDI | DMA_CH_VALID,
		.hw_addr.from	= S3C2410_PA_IIS + S3C2410_IISFIFO,
	},
	[DMACH_I2S_OUT] = {
		.name		= "i2s-sdo",
		.channels[0]	= S3C2440_DCON_CH0_I2SSDO | DMA_CH_VALID,
		.channels[2]	= S3C2410_DCON_CH2_I2SSDO | DMA_CH_VALID,
		.hw_addr.to	= S3C2410_PA_IIS + S3C2410_IISFIFO,
	},
	[DMACH_PCM_IN] = {
		.name		= "pcm-in",
		.channels[0]	= S3C2440_DCON_CH0_PCMIN | DMA_CH_VALID,
		.channels[2]	= S3C2440_DCON_CH2_PCMIN | DMA_CH_VALID,
		.hw_addr.from	= S3C2440_PA_AC97 + S3C_AC97_PCM_DATA,
	},
	[DMACH_PCM_OUT] = {
		.name		= "pcm-out",
		.channels[1]	= S3C2440_DCON_CH1_PCMOUT | DMA_CH_VALID,
		.channels[3]	= S3C2440_DCON_CH3_PCMOUT | DMA_CH_VALID,
		.hw_addr.to	= S3C2440_PA_AC97 + S3C_AC97_PCM_DATA,
	},
	[DMACH_MIC_IN] = {
		.name		= "mic-in",
		.channels[2]	= S3C2440_DCON_CH2_MICIN | DMA_CH_VALID,
		.channels[3]	= S3C2440_DCON_CH3_MICIN | DMA_CH_VALID,
		.hw_addr.from	= S3C2440_PA_AC97 + S3C_AC97_MIC_DATA,
	},
	[DMACH_USB_EP1] = {
		.name		= "usb-ep1",
		.channels[0]	= S3C2410_DCON_CH0_USBEP1 | DMA_CH_VALID,
	},
	[DMACH_USB_EP2] = {
		.name		= "usb-ep2",
		.channels[1]	= S3C2410_DCON_CH1_USBEP2 | DMA_CH_VALID,
	},
	[DMACH_USB_EP3] = {
		.name		= "usb-ep3",
		.channels[2]	= S3C2410_DCON_CH2_USBEP3 | DMA_CH_VALID,
	},
	[DMACH_USB_EP4] = {
		.name		= "usb-ep4",
		.channels[3]	= S3C2410_DCON_CH3_USBEP4 | DMA_CH_VALID,
	},
};

static void s3c2440_dma_select(struct s3c2410_dma_chan *chan,
			       struct s3c24xx_dma_map *map)
{
	chan->dcon = map->channels[chan->number] & ~DMA_CH_VALID;
}

static struct s3c24xx_dma_selection __initdata s3c2440_dma_sel = {
	.select		= s3c2440_dma_select,
	.dcon_mask	= 7 << 24,
	.map		= s3c2440_dma_mappings,
	.map_size	= ARRAY_SIZE(s3c2440_dma_mappings),
};

static struct s3c24xx_dma_order __initdata s3c2440_dma_order = {
	.channels	= {
		[DMACH_SDI]	= {
			.list	= {
				[0]	= 3 | DMA_CH_VALID,
				[1]	= 2 | DMA_CH_VALID,
				[2]	= 1 | DMA_CH_VALID,
				[3]	= 0 | DMA_CH_VALID,
			},
		},
		[DMACH_I2S_IN]	= {
			.list	= {
				[0]	= 1 | DMA_CH_VALID,
				[1]	= 2 | DMA_CH_VALID,
			},
		},
		[DMACH_I2S_OUT]	= {
			.list	= {
				[0]	= 2 | DMA_CH_VALID,
				[1]	= 1 | DMA_CH_VALID,
			},
		},
		[DMACH_PCM_IN] = {
			.list	= {
				[0]	= 2 | DMA_CH_VALID,
				[1]	= 1 | DMA_CH_VALID,
			},
		},
		[DMACH_PCM_OUT] = {
			.list	= {
				[0]	= 1 | DMA_CH_VALID,
				[1]	= 3 | DMA_CH_VALID,
			},
		},
		[DMACH_MIC_IN] = {
			.list	= {
				[0]	= 3 | DMA_CH_VALID,
				[1]	= 2 | DMA_CH_VALID,
			},
		},
	},
};

static int __init s3c2440_dma_add(struct sys_device *sysdev)
{
	s3c2410_dma_init();
	s3c24xx_dma_order_set(&s3c2440_dma_order);
	return s3c24xx_dma_init_map(&s3c2440_dma_sel);
}

static struct sysdev_driver s3c2440_dma_driver = {
	.add	= s3c2440_dma_add,
};

static int __init s3c2440_dma_init(void)
{
	return sysdev_driver_register(&s3c2440_sysclass, &s3c2440_dma_driver);
}

arch_initcall(s3c2440_dma_init);

入口：

arch_initcall(s3c2440_dma_init);

DMA驱动作为系统驱动由sysdev_driver_register来向内核注册，这里只关注s3c2440_dma_driver相关的内容，即调用drive中的add方法，其他的kobject对象略过。

s3c2440_dma_add做了一系列的初始化工作。调用如下三个函数

1.s3c2410_dma_init，利用平台资源初始化dma.

主要传递的参数：

unsigned int channels：

s3c2440平台对应的DMA通道总数，为4

unsigned int irq：起始DMA中断的中断号

unsigned int stride：每通道DMA所占寄存器资源数

其中struct s3c2410_dma_chan记录dma通道信息，这个数组是针对实际的硬件信息建立的，每个硬件的dma通道唯一对应一个struct s3c2410_dma_chan的数据结构。与之对应的还有一个虚拟的dma通道，其实质是将不同dma请求源区分开来，然后用一个虚拟的通道号与之一一对应，然后与实际的dma通道通过一张map表关联起来。

2.   s3c24xx_dma_order_set

首先这个函数的意义是预定一些目标板要用的dma通道，使用的是上文提到的虚拟的dma通道号。dma_order是个全局变量，其作用是记录下目标板的dma预定信息。

3.3.s3c24xx_dma_init_map

他实际是根据硬件情况为一个全局变量赋值。与前面的初始化一样，这里主要是为了统一管理plat24xx这个平台下的dma资源，所以不同的芯片必须将自己硬件有关的dma信息初始化到相应的全局变量中。再说函数之前先来关注一下struct s3c24xx_dma_map这个数据结构，他提供了dma虚拟通道与实际的dma通道直接的关联。

初始化的任务比较简单，就是

（1）建立硬件dma通道信息即：

struct s3c2410_dma_chan s3c2410_chans[S3C_DMA_CHANNELS];

（2）建立目标板虚拟dma通道与硬件的dma通道的关联：

static struct s3c24xx_dma_order *dma_order;

（3）建立芯片本身的虚拟dma通道与硬件dma通道的视图：

static struct s3c24xx_dma_selection dma_sel;

完成上述工作以后，基本的dma框架就已经建立起来了。

使用DMA功能主要涉及以下几个步骤：

1，申请DMA资源

   s3c2410_dma_request

2, DMA缓冲区的申请。

dma_alloc_coherent

3，DMA队列填充，linux对DMA使用一个队列进行管理，我们在申请了DMA通道以后接下来的工作就是向DMA缓冲区中填充数据，DMA传输数据问题交由linux来处理。

s3c2410_dma_enqueue

4.dma 释放

s3c2410_dma_free