Re: [PATCH] spi: pl022: Fix broken spidev when DMA is enabled

From: Ray Jui
Date: Wed Oct 08 2014 - 12:14:35 EST

On 10/8/2014 4:21 AM, Mark Brown wrote:
On Tue, Oct 07, 2014 at 09:38:47PM -0700, Ray Jui wrote:

The PL022 SPI driver maps the DMA RX buffer before the DMA TX buffer. In
most cases, the sequence of the mapping does not matter. But in cases
where TX and RX happen to use the same buffer, e.g., spidev, it causes
the cached TX data not written to memory, because the same memory has
been marked invalid when dma_map_sg on the RX buffer is called

This seems like it is a bug in spidev, using the same buffer simultaneously
for both directions isn't something I'd think would be expected to work
reliably unless it was explicitly mapped as bidirectional.

Hi Mark,

Thanks for the reply. It looks like you are also the maintainer of spidev. In this case, could you please help to confirm that you expect spidev to use separate buffers for TX and RX? If so, I can go ahead and make the change in spidev.

+ Grant


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