linux-kernel - Re: [PATCH] spi/pxa2xx: Prevent DMA from transferring too many bytes

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Message-ID: <20140509103315.GJ12304@sirena.org.uk>
Date:	Fri, 9 May 2014 11:33:15 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:	linux-kernel@...r.kernel.org, Eric Miao <eric.y.miao@...il.com>,
	Russell King <linux@....linux.org.uk>,
	Haojian Zhuang <haojian.zhuang@...il.com>,
	Chiau Ee Chew <chiau.ee.chew@...el.com>,
	Hock Leong Kweh <hock.leong.kweh@...el.com>
Subject: Re: [PATCH] spi/pxa2xx: Prevent DMA from transferring too many bytes

On Thu, May 08, 2014 at 05:30:31PM +0300, Mika Westerberg wrote:
> In case we are doing DMA transfer and the size of the buffer is not multiple
> of 4 bytes the driver truncates that to 4-byte boundary and tries to handle
> remaining bytes using PIO.

...

> While investigating this it turned out that the DMA hardware doesn't even
> have such limitation so we can solve this by dropping the code that tries
> to handle unaligned bytes.

Is this definitely the case for all of the IPs using this driver?  It
seems like something which might have been present in actual PXA
implemenetations but got fixed in later revisons used with x86.  Equally
well the current code is clearly broken either way so I'm not sure that
problems with older systems should be a barrier to merging the patch but
it seems better to check.

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