From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTP id EBEFCDDE23 for ; Tue, 19 Feb 2008 11:36:47 +1100 (EST) Subject: Re: [Linux-fbdev-devel] [PATCH 1/2] fb: add support for foreign endianness From: Benjamin Herrenschmidt To: Clemens Koller In-Reply-To: <47BA162C.5000807@anagramm.de> References: <20080205154432.GA8749@localhost.localdomain> <20080214224942.a0cb6218.akpm@linux-foundation.org> <20080215164542.GB16810@localhost.localdomain> <20080218081847.e9e65f2f.krzysztof.h1@poczta.fm> <19805.1203355811@turing-police.cc.vt.edu> <47BA162C.5000807@anagramm.de> Content-Type: text/plain Date: Tue, 19 Feb 2008 11:35:53 +1100 Message-Id: <1203381353.6740.59.camel@pasglop> Mime-Version: 1.0 Cc: linux-fbdev-devel@lists.sourceforge.net, adaplas@gmail.com, Krzysztof Helt , linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org, Geert Uytterhoeven , Andrew Morton Reply-To: benh@kernel.crashing.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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.