linux下面的驅(qū)動雖然什么樣的情形都有，但是dma驅(qū)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(shù)據(jù)搬來搬去，這個時候cpu就由時間去做別的事情了，提高了設(shè)備效率。
1、dma驅(qū)動在什么地方
drivers/dma
2、如何看s3c的dma驅(qū)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(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code獲悉，s3cdma有master和slave兩個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engine要進(jìn)行注冊使用。
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內(nèi)容，希望對大家的學(xué)習(xí)有所幫助，也希望大家多多支持VEVB武林網(wǎng)。
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