详解linux dma驱动编写
<p>linux下面的驱动虽然什么样的情形都有，但是dma驱动却并不少见。dma可以有很多的好处，其中最重要的功能就是能够帮助我们将数据搬来搬去，这个时候cpu就由时间去做别的事情了，提高了设备效率。</p>
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1、dma驱动在什么地方</p>
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<code class="plain plain">drivers/dma</code>
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<p>
2、如何看s3c的dma驱动，先看Kconfig</p>
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<code class="plain plain">config S3C24XX_DMAC </code>
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<code class="plain spaces"> </code><code class="plain plain">bool "Samsung S3C24XX DMA support" </code>
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<code class="plain spaces"> </code><code class="plain plain">depends on ARCH_S3C24XX || COMPILE_TEST </code>
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<code class="plain spaces"> </code><code class="plain plain">select DMA_ENGINE </code>
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<code class="plain spaces"> </code><code class="plain plain">select DMA_VIRTUAL_CHANNELS </code>
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<code class="plain spaces"> </code><code class="plain plain">help </code>
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<code class="plain spaces"> </code><code class="plain plain">Support for the Samsung S3C24XX DMA controller driver. The </code>
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<code class="plain spaces"> </code><code class="plain plain">DMA controller is having multiple DMA channels which can be </code>
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<code class="plain spaces"> </code><code class="plain plain">configured for different peripherals like audio, UART, SPI. </code>
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<code class="plain spaces"> </code><code class="plain plain">The DMA controller can transfer data from memory to peripheral, </code>
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<code class="plain spaces"> </code><code class="plain plain">periphal to memory, periphal to periphal and memory to memory. </code>
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<p>
3、发现s3c只依赖于S3C24XX_DMAC，这样可以接着看Makefile</p>
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<code class="plain plain">obj-$(CONFIG_S3C24XX_DMAC) += s3c24xx-dma.o</code>
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<p>
4、确认驱动文件为s3c24xx-dma.c，了解基本结构</p>
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<code class="cpp keyword bold">static</code> <code class="cpp keyword bold">struct</code> <code class="cpp plain">platform_driver s3c24xx_dma_driver = { </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.driver = { </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.name = </code><code class="cpp string">"s3c24xx-dma"</code><code class="cpp plain">, </code>
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<code class="cpp spaces"> </code><code class="cpp plain">}, </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.id_table = s3c24xx_dma_driver_ids, </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.probe = s3c24xx_dma_probe, </code>
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<code class="cpp spaces"> </code><code class="cpp plain">.</code><code class="cpp functions bold">remove</code> <code class="cpp plain">= s3c24xx_dma_remove, </code>
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<code class="cpp plain">}; </code>
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<code class="cpp spaces"> </code>
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<code class="cpp plain">module_platform_driver(s3c24xx_dma_driver); </code>
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<p>
5、驱动为基本的platform driver，接着就可以了解probe函数了</p>
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<code class="cpp comments">/* Initialize memcpy engine */</code>
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<code class="cpp plain">dma_cap_set(DMA_MEMCPY, s3cdma-></code><code class="cpp functions bold">memcpy</code><code class="cpp plain">.cap_mask); </code>
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<code class="cpp plain">dma_cap_set(DMA_PRIVATE, s3cdma-></code><code class="cpp functions bold">memcpy</code><code class="cpp plain">.cap_mask); </code>
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<code class="cpp plain">s3cdma-></code><code class="cpp functions bold">memcpy</code><code class="cpp plain">.dev = &pdev->dev; </code>
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<code class="cpp plain">s3cdma-></code><code class="cpp functions bold">memcpy</code><code class="cpp plain">.device_free_chan_resources = </code>
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<code class="cpp spaces"> </code><code class="cpp plain">s3c24xx_dma_free_chan_resources; </code>
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<code class="cpp plain">s3cdma-></code><code class="cpp functions bold">memcpy</code><code class="cpp plain">.device_prep_dma_memcpy = s3c24xx_dma_prep_memcpy; </code>
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<code class="cpp plain">s3cdma-></code><code class="cpp functions bold">memcpy</code><code class="cpp plain">.device_tx_status = s3c24xx_dma_tx_status; </code>
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<code class="cpp plain">s3cdma-></code><code class="cpp functions bold">memcpy</code><code class="cpp plain">.device_issue_pending = s3c24xx_dma_issue_pending; </code>
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<code class="cpp plain">s3cdma-></code><code class="cpp functions bold">memcpy</code><code class="cpp plain">.device_config = s3c24xx_dma_set_runtime_config; </code>
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<code class="cpp plain">s3cdma-></code><code class="cpp functions bold">memcpy</code><code class="cpp plain">.device_terminate_all = s3c24xx_dma_terminate_all; </code>
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<code class="cpp plain">s3cdma-></code><code class="cpp functions bold">memcpy</code><code class="cpp plain">.device_synchronize = s3c24xx_dma_synchronize; </code>
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<code class="cpp spaces"> </code>
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<code class="cpp comments">/* Initialize slave engine for SoC internal dedicated peripherals */</code>
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<code class="cpp plain">dma_cap_set(DMA_SLAVE, s3cdma->slave.cap_mask); </code>
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<code class="cpp plain">dma_cap_set(DMA_CYCLIC, s3cdma->slave.cap_mask); </code>
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<code class="cpp plain">dma_cap_set(DMA_PRIVATE, s3cdma->slave.cap_mask); </code>
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<code class="cpp plain">s3cdma->slave.dev = &pdev->dev; </code>
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<code class="cpp plain">s3cdma->slave.device_free_chan_resources = </code>
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<code class="cpp spaces"> </code><code class="cpp plain">s3c24xx_dma_free_chan_resources; </code>
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<code class="cpp plain">s3cdma->slave.device_tx_status = s3c24xx_dma_tx_status; </code>
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<code class="cpp plain">s3cdma->slave.device_issue_pending = s3c24xx_dma_issue_pending; </code>
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<code class="cpp plain">s3cdma->slave.device_prep_slave_sg = s3c24xx_dma_prep_slave_sg; </code>
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<code class="cpp plain">s3cdma->slave.device_prep_dma_cyclic = s3c24xx_dma_prep_dma_cyclic; </code>
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<code class="cpp plain">s3cdma->slave.device_config = s3c24xx_dma_set_runtime_config; </code>
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<code class="cpp plain">s3cdma->slave.device_terminate_all = s3c24xx_dma_terminate_all; </code>
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<code class="cpp plain">s3cdma->slave.device_synchronize = s3c24xx_dma_synchronize; </code>
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<code class="cpp plain">s3cdma->slave.filter.map = pdata->slave_map; </code>
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<code class="cpp plain">s3cdma->slave.filter.mapcnt = pdata->slavecnt; </code>
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<code class="cpp plain">s3cdma->slave.filter.fn = s3c24xx_dma_filter; </code>
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<p>
6、通过code获悉，s3cdma有master和slave两个engine，且部分接口共享。</p>
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只要完成dma接口的适配，dma就可以正常使用了。当然，前提是，两个engine要进行注册使用。</p>
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<code class="cpp plain">ret = dma_async_device_register(&s3cdma-></code><code class="cpp functions bold">memcpy</code><code class="cpp plain">); </code>
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<code class="cpp keyword bold">if</code> <code class="cpp plain">(ret) { </code>
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<code class="cpp spaces"> </code><code class="cpp plain">dev_warn(&pdev->dev, </code>
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<code class="cpp spaces"> </code><code class="cpp string">"%s failed to register memcpy as an async device - %d\n"</code><code class="cpp plain">, </code>
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<code class="cpp spaces"> </code><code class="cpp plain">__func__, ret); </code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">goto</code> <code class="cpp plain">err_memcpy_reg; </code>
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<code class="cpp plain">} </code>
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<code class="cpp spaces"> </code>
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<code class="cpp plain">ret = dma_async_device_register(&s3cdma->slave); </code>
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<code class="cpp keyword bold">if</code> <code class="cpp plain">(ret) { </code>
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<code class="cpp spaces"> </code><code class="cpp plain">dev_warn(&pdev->dev, </code>
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<code class="cpp spaces"> </code><code class="cpp string">"%s failed to register slave as an async device - %d\n"</code><code class="cpp plain">, </code>
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<code class="cpp spaces"> </code><code class="cpp plain">__func__, ret); </code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">goto</code> <code class="cpp plain">err_slave_reg; </code>
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<code class="cpp plain">} </code>
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<p>
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。</p>
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原文链接：https://blog.csdn.net/feixiaoxing/article/details/79873782</p>
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