Re: [PATCH 1/2] fb: add support for foreign endianness

On Tue, 2008-02-19 at 00:35 +0100, Clemens Koller wrote:

Valdis.Kletnieks@vt.edu schrieb:

quoted

On Mon, 18 Feb 2008 08:18:47 +0100, Krzysztof Helt said:

quoted

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.

Then there is also the risk that your PCI<->Localbus has been wired
improperly :-)

Ben.



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