Messages in this thread | | | Subject | Re: [Linux-fbdev-devel] [PATCH 1/2] fb: add support for foreign endianness | From | Benjamin Herrenschmidt <> | Date | Tue, 19 Feb 2008 11:35:53 +1100 |
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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.
Then there is also the risk that your PCI<->Localbus has been wired improperly :-)
Ben.
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