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

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Message-ID: <20141008112143.GT4609@sirena.org.uk>
Date:	Wed, 8 Oct 2014 12:21:43 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Ray Jui <rjui@...adcom.com>
Cc:	linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org,
	JD Zheng <jdzheng@...adcom.com>,
	Scott Branden <sbranden@...adcom.com>
Subject: Re: [PATCH] spi: pl022: Fix broken spidev when DMA is enabled

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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