Shulou(Shulou.com)06/02 Report--

Although there are all kinds of drivers under linux, dma drivers are not uncommon. Dma can have many benefits, of which the most important function is to help us move data around. At this time, cpu will have time to do something else and improve the efficiency of the device.

1. Where is the dma driver

Drivers/dma

2. How to look at the dma driver of S3C, take a look at Kconfig first

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. It is found that S3C only depends on S3C24XX_DMAC, so you can move on to Makefile.

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

4. Confirm that the driver file is s3c24xx-dma.c and understand the basic structure.

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. The driver is the basic platform driver, and then you can understand the probe function.

/ * Initialize memcpy engine * / dma_cap_set (DMA_MEMCPY, s3cdmaa-> memcpy.cap_mask); dma_cap_set (DMA_PRIVATE, s3cdmaa-> memcpy.cap_mask); s3cdma-> memcpy.dev = & pdev- > dev; s3cdma-> memcpy.device_free_chan_resources = s3c24xroomdmah freefreehands; s3cdma-> memcpy.device_prep_dma_memcpy = s3c24xprepares memcpyy; s3cdma-> memcpy.device_tx_status = s3c24xx_dma_tx_status S3cdmaa-> memcpy.device_issue_pending = s3c24xxroomdmaissuing issuing; s3cdmaa-> memcpy.device_config = s3c24xxperfect setting setting runtimefilling config.s3cdmaa-> memcpy.device_terminate_all = s3c24xroomdmaxed terminating all; s3cdmaa-> memcpy.device_synchronize = s3c24xroomdmaxed synchronization; / * Initialize slave engine for SoC internal dedicated peripherals * / dma_cap_set (DMA_SLAVE, s3cdma-> slave.cap_mask); dma_cap_set (DMA_CYCLIC, s3cdmaa-> slave.cap_mask) Dma_cap_set (DMA_PRIVATE, s3cdmaa-> slave.cap_mask); s3cdmaa-> slave.dev = & pdev- > dev; s3cdmaa-> slave.device_free_chan_resources = s3c24xroomdmafree freechanagesresourcess3cdmaa-> slave.device_tx_status = s3c24xroomdmaissuing status; s3cdmaa-> slave.device_issue_pending = s3c24xxroomdmaissuing issuing; s3cdmaa-> slave.device_prep_slave_sg = s3c24xx_dma_prep_slave_sg S3cdmaa-> slave.device_prep_dma_cyclic = s3c24xxprepared dmakeshift cyclical; s3cdmaa-> slave.device_config = s3c24xxqualified dmaThe setsetsetting runtimekeeper config.s3cdmaa-> slave.device_terminate_all = s3c24xxroomdmaterminatesynchronized all; s3cdmaa-> slave.device_synchronize = s3c24xxreserved dmaxed synchronized; s3cdmaa-> slave.filter.map = pdata- > slave_map; s3cdmaa-> slave.filter.mapcnt = pdata- > slavecnt; s3cdmaa-> slave.filter.fn = s3c24xx_dma_filter

6. Learn from code that s3cdma has two engine, master and slave, and some of the interfaces are shared.

As long as the adaptation of the dma interface is completed, dma can be used normally. Of course, the premise is that both engine are registered for use.

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;}

The above is the whole content of this article, I hope it will be helpful to your study, and I also hope that you will support it.

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