From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752259AbVHGQSb (ORCPT ); Sun, 7 Aug 2005 12:18:31 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752260AbVHGQSb (ORCPT ); Sun, 7 Aug 2005 12:18:31 -0400 Received: from gate.crashing.org ([63.228.1.57]:55508 "EHLO gate.crashing.org") by vger.kernel.org with ESMTP id S1752258AbVHGQSa (ORCPT ); Sun, 7 Aug 2005 12:18:30 -0400 Subject: Re: Regression: radeonfb: No synchronisation on CRT with linux-2.6.13-rc5 From: Benjamin Herrenschmidt To: Kyle Moffett Cc: Bodo Eggert <7eggert@gmx.de>, LKML , linux-fbdev-devel@lists.sourceforge.net In-Reply-To: <3EF2003B-12DF-4EBB-B304-59614AEFAA09@mac.com> References: <1123195493.30257.75.camel@gaston> <1123401069.30257.102.camel@gaston> <3EF2003B-12DF-4EBB-B304-59614AEFAA09@mac.com> Content-Type: text/plain Date: Sun, 07 Aug 2005 18:13:38 +0200 Message-Id: <1123431219.30257.115.camel@gaston> Mime-Version: 1.0 X-Mailer: Evolution 2.2.2 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org > I'm having a similar issue with my shiny new 17" Powerbook G4. The > radeon chip works fine with framebuffer in 2.6.12.4 _with_ PREEMPT, > but not in 2.6.13-rc5 _with_ PREEMPT (configs are virtually identical). > I'll try your idea this afternoon when I get the chance. Note that PREEMPT is known to cause problems on ppc32 ... I'm not sure what's up yet. (Random SIGILLs/SEGVs in userland typically) > I wonder if perhaps some code in radeonfb is used under the BKL, which > is now preemptable (Or maybe an ordinary spinlock changed or went > away?), because I also set PREEMPT_BKL. radeonfb should only rely on the console semaphore.... > I've got an LCD, and on mine > it looks like every third pixel-line gets shifted about 32-64 pixels to > the left, and they move with display refresh. My guess is that > something is interrupting radeonfb during a critical time in display > syncing and forcing the video card to wait too far into the next line > before sending pixels. radeonfb is mostly inactive after it has setup the framebuffer and unless you actually draw something, in which case, accel code is called. _However_ there is an unrelated problem with some panels, including some of the 17": The panel doesn't always "sync" properly. This seem to be related to some subtle timing issue in the LVDS code but I don't know exactly what yet. You can usually get it back by repeately turning the backlight all the way down (which shuts the panel off) and back up until it "catches". > One other data point, I've seen something like this, except not nearly > as bad, is stock debian 2.6.8 vs. stock debian 2.6.11 on powerpc. The > former exhibits some similar (but not nearly as bad) symptoms. (Same > Powerbook), whereas 2.6.11 doesn't. In that case, neither has PREEMPT. > I'll run more tests this afternoon/evening, to try to track it down. > > Cheers, > Kyle Moffett > > -- > There are two ways of constructing a software design. One way is to > make it so > simple that there are obviously no deficiencies. And the other way is > to make > it so complicated that there are no obvious deficiencies. The first > method is > far more difficult. > -- C.A.R. Hoare >