Linux/AM5728: How can I use DMA to move and disperse memory?

Hi Tian,

Check if DMA_INTERLEAVE dma transaction type will be in help for your use case.

Supported transaction types

DMA_INTERLEAVE

   The device supports interleaved transfer.

   These transfers can transfer data from a non-contiguous buffer to a non-contiguous buffer, opposed to DMA_SLAVE that can transfer data from a non-contiguous data set to a continuous destination buffer.

   It’s usually used for 2d content transfers, in which case you want to transfer a portion of uncompressed data directly to the display to print it

 

DMA_SLAVE might also work for you:

 

Our theoretical DMA controller would then only be able to do transfers that involve a single contiguous block of data. However, some of the transfers we usually have are not, and want to copy data from non-contiguous buffers to a contiguous buffer, which is called scatter-gather.

 

DMA_SLAVE

The device can handle device to memory transfers, including scatter-gather transfers.

 

Regards,
Pavel

Hi:

Thank you very much for your reply.

DMA_SLAVE is MEM_TO_DEVICE or DEVICE_TO_MEM transmission mode, and I want MEM_TO_MEM

1、I use the dmatest test DMA in the SDK4.3 kernel.

dmatest.c file directory “~/ti-processor-sdk-linux-am57xx-evm-04.03.00.05/board-support/linux-4.9.69+gitAUTOINC+9ce43c71ae-g9ce43c71ae/drivers/dma/dmatest.c”

dmatest can test DMA the following transmission methods

DMA_MEMCPY

DMA_SG

DMA_XOR

DMA_PQ

When I use the DMA_MEMCPY transfer method, I can pass the test, and the DMA_SG, DMA_XOR, and DMA_PQ transfer mode tests fail. And I want to use the DMA_SG method for transmission. help me?

 

Run the following command：

root@am57xx-evm:~# modprobe dmatest

root@am57xx-evm:~# echo dma0chan0 > /sys/module/dmatest/parameters/channel

root@am57xx-evm:~# echo 2000 > /sys/module/dmatest/parameters/timeout

root@am57xx-evm:~# echo 1 > /sys/module/dmatest/parameters/iterations

root@am57xx-evm:~# echo 1 > /sys/module/dmatest/parameters/run

 2、Can you give a test SLAVE_SG example? thank you very much.

Thanks

Tain,

Yes, dmatest do not support SG (scatter gather) mode. You should update this test per your needs.

See if below patch will be in help:

patchwork.kernel.org/.../

Another approach you can try is to apply DMA_MEMSET_SG mode in dmatest file, you can see how DMA_MEMSET is implemented and reuse that approach for DMA_MEMSET_SG. You can even try to transform DMA_MEMSET_SG to custom DMA_MEMCPY_SG mode. DMA_MEMSET mode is available in dmatest.c in kernel 4.14.79 (PSDK v5.02), I am not sure for older kernels.

For slave_sg example, I can provide only memory-to-device and device-to-memory example, I have no memory-to-memory example. See below:

linux-kernel/drivers/spi/spi-omap2-mcspi.c
linux-kernel/drivers/mtd/nand/omap2.c

Regards,
Pavel