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詳解linux dma驅(qū)動(dòng)編寫(xiě)

更新時(shí)間：2018年04月11日 10:09:41 作者：feixiaoxing

這篇文章主要介紹了詳解linux dma驅(qū)動(dòng)編寫(xiě)，小編覺(jué)得挺不錯(cuò)的，現(xiàn)在分享給大家，也給大家做個(gè)參考。一起跟隨小編過(guò)來(lái)看看吧

linux下面的驅(qū)動(dòng)雖然什么樣的情形都有，但是dma驅(qū)動(dòng)卻并不少見(jiàn)。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(shù)據(jù)搬來(lái)搬去，這個(gè)時(shí)候cpu就由時(shí)間去做別的事情了，提高了設(shè)備效率。

1、dma驅(qū)動(dòng)在什么地方

drivers/dma

2、如何看s3c的dma驅(qū)動(dòng)，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(fā)現(xiàn)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(rèn)驅(qū)動(dòng)文件為s3c24xx-dma.c，了解基本結(jié)構(gòu)

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(qū)動(dòng)為基本的platform driver，接著就可以了解probe函數(shù)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;

6、通過(guò)code獲悉，s3cdma有master和slave兩個(gè)engine，且部分接口共享。

只要完成dma接口的適配，dma就可以正常使用了。當(dāng)然，前提是，兩個(gè)engine要進(jìn)行注冊(cè)使用。

ret = dma_async_device_register(&s3cdma->memcpy); 
if (ret) { 
  dev_warn(&pdev->dev, 
    "%s failed to register memcpy as an async device - %d\n", 
    __func__, ret); 
  goto err_memcpy_reg; 
} 
 
ret = dma_async_device_register(&s3cdma->slave); 
if (ret) { 
  dev_warn(&pdev->dev, 
    "%s failed to register slave as an async device - %d\n", 
    __func__, ret); 
  goto err_slave_reg; 
}

以上就是本文的全部?jī)?nèi)容，希望對(duì)大家的學(xué)習(xí)有所幫助，也希望大家多多支持腳本之家。

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