linux-kernel - Re: 6175ddf06b6172046a329e3abfd9c901a43efd2e breaks matroxfb console

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Message-ID: <4C573575.8040701@zytor.com>
Date:	Mon, 02 Aug 2010 14:15:33 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ondrej Zary <linux@...nbow-software.org>
CC:	brgerst@...il.com,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: 6175ddf06b6172046a329e3abfd9c901a43efd2e breaks matroxfb console

On 08/02/2010 02:14 PM, Ondrej Zary wrote:
> On Monday 02 August 2010 23:04:28 H. Peter Anvin wrote:
>> On 08/02/2010 12:49 PM, Ondrej Zary wrote:
>>> Hello,
>>> matroxfb (at least with Mystique and Mystique 220) stopped working in
>>> 2.6.34 - the screen is completely corrupted. Bisection shows that
>>> 6175ddf06b6172046a329e3abfd9c901a43efd2e is first bad commit.
>>>
>>> Reverting 6175ddf06b6172046a329e3abfd9c901a43efd2e in 2.6.34 fixes the
>>> problem (1c5b9069e12e20d2fe883076ae0bf73966492108 must be reverted
>>> first).
>>
>> Sounds like another driver which used memcpy_toio() when it should have
>> used iowrite32_rep() or __iowrite32_copy().
>>
>> Hmm... is __iowrite32_copy() and iowrite32_rep() redundant?  If so, we
>> should get rid of the former.
> 
> There is a wrapper in drivers/video/matrox/matroxfb_base.h (see below) with
> some comment. So this commit changed one of the three points?
> 
> static inline void mga_memcpy_toio(vaddr_t va, const void* src, int len) {
> #if defined(__alpha__) || defined(__i386__) || defined(__x86_64__)
>         /*
>          * memcpy_toio works for us if:
>          *  (1) Copies data as 32bit quantities, not byte after byte,
>          *  (2) Performs LE ordered stores, and
>          *  (3) It copes with unaligned source (destination is guaranteed to be page
>          *      aligned and length is guaranteed to be multiple of 4).
>          */
>         memcpy_toio(va.vaddr, src, len);
> #else

Yes, point (1) is not guaranteed by memcpy_toio().

	-hpa
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