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

From: Mark Brown
Date: Wed Oct 08 2014 - 07:22:16 EST

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.

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