如何通过DMA从RAM到RAM传输数据? [英] How to transfer data via DMA from RAM to RAM?

问题描述

我想编写一个内核模块，该模块可以通过DMA从RAM到RAM传输数据.有一些讨论这个问题的帖子，但是我真的不明白.有人说可能别人说不是.

I want to write a kernel module that can transfer data via DMA from RAM to RAM. There are some posts that discuss this, but I don't really get it. Some say it is possible others say it isn’t.

如果我对ldd3的理解正确，那么使用Linux的DMA API无法将RAM复制到RAM，但是 driver/dma/dmaengine.c 为"DMA传输类型"提供了标志DMA_MEMCPY ，所以应该有办法.

If I understood ldd3 right, RAM to RAM copying isn‘t possible with the DMA API of linux, but the driver/dma/dmaengine.c provides a flag DMA_MEMCPY for a "DMA Transfer Type", so there should be a way.

这是正确的吗，我可以使用dma引擎将数据从一个ram地址传输到另一个ram地址吗?

Is this correct, can I use a dma engine to transfer data from one ram address to another?

如果取决于硬件，如何确定我的系统是否支持dma memcpy?

If it is hardware dependent, how can I determine if my system supports dma memcpy?

推荐答案

正如您正确指出的那样，应使用DMA_MEMCPY执行RAM到RAM的复制.在 Documentation/dmaengine/provider.txt 中进行了描述. .这只是一个相关摘录，请查看整个文件以了解更多详细信息:

As you correctly pointed out, DMA_MEMCPY should be used to perform RAM-to-RAM copy. It is described in Documentation/dmaengine/provider.txt. Here is just a related excerpt, please see the whole file for more details:

支持的交易类型

下一步，您需要设置设备的交易类型 (和驱动程序)支持.

Supported transaction types

The next thing you need is to set which transaction types your device (and driver) supports.

我们的dma_device结构具有一个名为cap_mask的字段，其中包含 支持各种类型的交易，您需要对此进行修改 使用dma_cap_set功能的蒙版，取决于 您支持作为参数的交易类型.

Our dma_device structure has a field called cap_mask that holds the various types of transaction supported, and you need to modify this mask using the dma_cap_set function, with various flags depending on transaction types you support as an argument.

所有这些功能都在dma_transaction_type枚举中定义， 在include/linux/dmaengine.h

All those capabilities are defined in the dma_transaction_type enum, in include/linux/dmaengine.h

当前，可用的类型为:

• DMA_MEMCPY
  • 该设备能够执行内存到内存副本
  • DMA_MEMCPY
    • The device is able to do memory to memory copies

    总结一下:

    • 这取决于您的DMA控制器.有些可以做到RAM到RAM的事务，有些则不能.

    • It depends on your DMA controller. Some are able to do RAM-to-RAM transaction, some aren't.

    例如，对于基于OMAP的SoC，DMA控制器执行此操作(drivers/dma/omap-dma.c文件，在omap_dma_probe()函数中):

    For example, for OMAP-based SoCs, DMA controller does this (drivers/dma/omap-dma.c file, in omap_dma_probe() function):

    dma_cap_set(DMA_MEMCPY, od->ddev.cap_mask);
    

  • 这样，您以后便可以在驱动程序中对其进行检查(如果DMA控制器能够进行RAM到RAM的事务).在dmatest_add_channel()函数的drivers/dma/dmatest.c中查看其操作方式:

  • This way you can later check it (if your DMA controller is capable of RAM-to-RAM transactions) in your driver. See how it's done in drivers/dma/dmatest.c, in dmatest_add_channel() function:

    if (dma_has_cap(DMA_MEMCPY, dma_dev->cap_mask)) {
    

  如果您需要有关如何使用DMA API执行RAM到RAM事务的示例，请参见

  If you need an example on how to use DMA API to perform RAM-to-RAM transaction, please see drivers/dma/dmatest.c.

  这篇关于如何通过DMA从RAM到RAM传输数据?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！