AM335x + gpmc + prefetch-dma + edma

Hi Jacob,

This forum supports only the TI released Linux SDK, currently v3.14.26. Supported transfer modes can be seen here: http://processors.wiki.ti.com/index.php/Linux_Core_NAND_User's_Guide#Choose_correct_bus_transfer_mode

The wiki link I sent you is for the NAND driver included in v3.14.26. I can't say anything about v4.2, this is not supported by TI.

Hi Biser!

I have compared the TI v3.14.26 code  with 4.2+ and it's very similar:

info->dma = dma_request_channel(mask, omap_dma_filter_fn, &sig);
if (!info->dma) {
    dev_err(&pdev->dev, "DMA engine request failed\n");
    err = -ENXIO;
    goto return_error;

Where omap_dma_filter_fn is defined in drivers/dma/omap-dma.c and again, seems to be only for SDMA. Can you confirm that this setup actually works?

Thanks, Jacob

i encounter the same problem.

do you have solve the "prefetch-dma"?

we use linux-3.14.26 from TI

Yordan, I believe it's reasonable to get a reply on this now.

I believe the code clearly says that it's not supported. Can you confirm that you have a system running with prefetch-dma working?

Thanks, Jacob

The am335x must use dma channel 52 which is assigned to gpmc. A function like this makes this assignment:

   info->dma = of_dma_request_slave_channel(pdata->of_node, "rxtx");

and in the dts file the dma configuration must be added to the nand node:

   dmas = <&edma 52>;
   dma-names = "rxtx";

This way I got the dma channel correctly assigned.

However there is a problem with the read from nand. When I use the nanddump the system freezes waiting for the prefetch engine event.
With the devmem2 I am able to trigger manually the event and the dma reads 128 bytes from the prefetch fifo. Repeating the manual trigger causes the
nanddump to finish correctly.
The fifo threshold is set to 64 bytes so it looks like the manual trigger causes the dma to read 64 bytes from the fifo and then the dma receives a hardware event
from the gpmc prefetch engine which causes the dma to read next 64 bytes, but after that the dma does not receive any further events. In my understanding
the dma should receive an event every time the fifo crosses the 64 byte threshold, but that does not happens.
Maybe the dma config is not correct, but the datasheet gives very little information about how to setup prefetch engine in dma mode.

Prefetch + DMA is running fine here.

Have you read this: