linux下面的驅動雖然什么樣的情形都有，但是dma驅動卻并不少見。dma可以有很多的好處，其中最重要的功能就是能夠幫助我們將數據搬來搬去，這個時候cpu就由時間去做別的事情了，提高了設備效率。

1、dma驅動在什么地方

drivers/dma 

2、如何看s3c的dma驅動，先看Kconfig

config S3C24XX_DMAC   bool "Samsung S3C24XX DMA support"   depends on ARCH_S3C24XX || COMPILE_TEST   select DMA_ENGINE   select DMA_VIRTUAL_CHANNELS   help    Support for the Samsung S3C24XX DMA controller driver. The    DMA controller is having multiple DMA channels which can be    configured for different peripherals like audio, UART, SPI.    The DMA controller can transfer data from memory to peripheral,    periphal to memory, periphal to periphal and memory to memory. 

3、發現s3c只依賴于S3C24XX_DMAC，這樣可以接著看Makefile

obj-$(CONFIG_S3C24XX_DMAC) += s3c24xx-dma.o 

4、確認驅動文件為s3c24xx-dma.c，了解基本結構

static struct platform_driver s3c24xx_dma_driver = {   .driver   = {     .name  = "s3c24xx-dma",   },   .id_table  = s3c24xx_dma_driver_ids,   .probe   = s3c24xx_dma_probe,   .remove   = s3c24xx_dma_remove, };  module_platform_driver(s3c24xx_dma_driver); 

5、驅動為基本的platform driver，接著就可以了解probe函數了

/* Initialize memcpy engine */ dma_cap_set(DMA_MEMCPY, s3cdma->memcpy.cap_mask); dma_cap_set(DMA_PRIVATE, s3cdma->memcpy.cap_mask); s3cdma->memcpy.dev = &pdev->dev; s3cdma->memcpy.device_free_chan_resources =         s3c24xx_dma_free_chan_resources; s3cdma->memcpy.device_prep_dma_memcpy = s3c24xx_dma_prep_memcpy; s3cdma->memcpy.device_tx_status = s3c24xx_dma_tx_status; s3cdma->memcpy.device_issue_pending = s3c24xx_dma_issue_pending; s3cdma->memcpy.device_config = s3c24xx_dma_set_runtime_config; s3cdma->memcpy.device_terminate_all = s3c24xx_dma_terminate_all; s3cdma->memcpy.device_synchronize = s3c24xx_dma_synchronize;  /* Initialize slave engine for SoC internal dedicated peripherals */ dma_cap_set(DMA_SLAVE, s3cdma->slave.cap_mask); dma_cap_set(DMA_CYCLIC, s3cdma->slave.cap_mask); dma_cap_set(DMA_PRIVATE, s3cdma->slave.cap_mask); s3cdma->slave.dev = &pdev->dev; s3cdma->slave.device_free_chan_resources =         s3c24xx_dma_free_chan_resources; s3cdma->slave.device_tx_status = s3c24xx_dma_tx_status; s3cdma->slave.device_issue_pending = s3c24xx_dma_issue_pending; s3cdma->slave.device_prep_slave_sg = s3c24xx_dma_prep_slave_sg; s3cdma->slave.device_prep_dma_cyclic = s3c24xx_dma_prep_dma_cyclic; s3cdma->slave.device_config = s3c24xx_dma_set_runtime_config; s3cdma->slave.device_terminate_all = s3c24xx_dma_terminate_all; s3cdma->slave.device_synchronize = s3c24xx_dma_synchronize; s3cdma->slave.filter.map = pdata->slave_map; s3cdma->slave.filter.mapcnt = pdata->slavecnt; s3cdma->slave.filter.fn = s3c24xx_dma_filter;