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

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Message-ID: <20140509112105.GS3722@lahna.fi.intel.com>
Date:	Fri, 9 May 2014 14:21:05 +0300
From:	Mika Westerberg <mika.westerberg@...ux.intel.com>
To:	Mark Brown <broonie@...nel.org>
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 Fri, May 09, 2014 at 11:33:15AM +0100, Mark Brown wrote:
> 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.

This code came with x86 LPSS implementation originally. The PXA one,
which lives in a different file (spi-pxa2xx-pxadma.c) didn't have any
such checks AFAIK.
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