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From: Clemens Koller <clemens.koller@anagramm.de>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: benh@kernel.crashing.org,
	linux-fbdev-devel@lists.sourceforge.net, adaplas@gmail.com,
	Krzysztof Helt <krzysztof.h1@poczta.fm>,
	linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Anton Vorontsov <avorontsov@ru.mvista.com>,
	valdis.kletnieks@vt.edu
Subject: Re: [Linux-fbdev-devel] [PATCH 1/2] fb: add support for foreign endianness
Date: Tue, 19 Feb 2008 13:22:02 +0100	[thread overview]
Message-ID: <47BAC9EA.1070305@anagramm.de> (raw)
In-Reply-To: <20080219040530.7b1d115d.akpm@linux-foundation.org>

Andrew Morton schrieb:
> On Tue, 19 Feb 2008 12:27:54 +0100 Clemens Koller <clemens.koller@anagramm.de> wrote:
>> Benjamin Herrenschmidt schrieb:
>>> On Tue, 2008-02-19 at 00:35 +0100, Clemens Koller wrote:
>>>> Valdis.Kletnieks@vt.edu schrieb:
>>>>> On Mon, 18 Feb 2008 08:18:47 +0100, Krzysztof Helt said:
>>>>>> I know two fb drivers which use endianess information (pm2fb and s3c2410fb).
>>>>>> Both resolve endianess at driver level. Actually, both handle it by setting special
>>>>>> bits so the graphics chip itself reorder bytes to transform foreign endianess. 
>>>>>> I understand that this patch is for chips which cannot reorder bytes by themselves.
>>>>> Does anybody know of such a chip that's actually available in the wild?  Or are
>>>>> we writing drivers for speculative possible chips?
>>>>>
>>>> I had troubles with the Silicon Motion SM501/SM502 endianess on PowerPC PCI vs. LocalBus.
>>>> The chip also has a register to swap endianess, but that seems to only affect some
>>>> LocalBus modes.
>>>> The current fb and X drivers are working, but when it comes to font
>>>> aliasing and hw-acceleration, the problems start to rise again...
>>> Most "sane" gfx chips nowadays provide configurable surfaces that allow
>>> to perform the swap when writing/reading from regions of the
>>> framebuffer, with the ability to set a different swapper setting (based
>>> on bit depth) per region.
>> Most! But not the SM50x. I still hope I would be wrong here. :-(
>>
>>> Then there is also the risk that your PCI<->Localbus has been wired
>>> improperly :-)
>> That's not an issue in my case. The SM50x can be connected to
>> either an PCI or some Local/CPU-whateverbus IF.
>> I.e. on the MPC85xx PowerPC, PCI and LocalBus are separate bussses.
>> If the sm501 is attached to the MPC85xx' PCI like any other video card,
>> the PCI config-space is can be accessed as usual, whereas the framebuffer
>> memory area is byte-swapped compared to other common video cards.
>>
>> So, to get back on topic:
>> I would welcome endianess swapping in SW. Some architectures (PowerPC)
>> should also be able to do swapped-endian mmapping. I just haven't
>> had time for a closer look but it looks also interesting way to do it
>> that way.
> 
> Bizarrely, the original author of the patch (Anton) has fallen off the cc. 
> Could whoever did that please thwap himself?

Propably my bad, being subscribed to several CCed lists...

> Anyway, my head is now officially spinning.  Did anyone actually have a
> reason why we shouldn't proceed with Anton's patch?

Since it seem that there are some odd chips out in the wild, I guess
Valdis (also readded to CC:) has no more objections to give it a try. :-)

Regards,

Clemens

  reply	other threads:[~2008-02-19 12:22 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-05 15:44 Anton Vorontsov
2008-02-05 19:07 ` Anton Vorontsov
2008-02-15  6:49 ` Andrew Morton
2008-02-15 16:45   ` Anton Vorontsov
2008-02-17  9:44     ` [Linux-fbdev-devel] " Geert Uytterhoeven
2008-02-18  7:18       ` Krzysztof Helt
2008-02-18 17:30         ` Valdis.Kletnieks
2008-02-18 17:37           ` Anton Vorontsov
2008-02-18 23:35           ` Clemens Koller
2008-02-19  0:35             ` Benjamin Herrenschmidt
2008-02-19 11:27               ` Clemens Koller
2008-02-19 12:05                 ` Andrew Morton
2008-02-19 12:22                   ` Clemens Koller [this message]
2008-02-20  0:47                   ` Valdis.Kletnieks
2008-02-20  0:50                     ` Benjamin Herrenschmidt
2008-02-20  0:56                   ` Paul Mackerras
2008-02-20 12:18                     ` Anton Vorontsov
2008-02-20 20:38                       ` Benjamin Herrenschmidt
2008-02-21  4:59                       ` Paul Mackerras
2008-02-20 15:43                     ` Clemens Koller
2008-02-16 11:49 ` Benjamin Herrenschmidt

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