https://bugs.freedesktop.org/show_bug.cgi?id=29726
Summary: New CRTC ID query breaks Radeon DRM in Zaphod mode Product: DRI Version: unspecified Platform: x86-64 (AMD64) OS/Version: Linux (All) Status: NEW Severity: normal Priority: medium Component: DRM/Radeon AssignedTo: dri-devel@lists.freedesktop.org ReportedBy: chewi@aura-online.co.uk
Created an attachment (id=38044) --> (https://bugs.freedesktop.org/attachment.cgi?id=38044) Patch against 2.6.35.3 to remove the offending code
Since upgrading from 2.6.34, programs such as Neverball and MythTV have only updated the screen while moving the mouse or pressing keys. I managed to bisect the kernel back to the infamous commit bc35afdb182d4c48c889fe27ba7a5d7ea0c8194d, along with its related fix 0baf2d8fe43fdd81faa30e65ff71785c99c78520. These add support for querying the hardware CRTC ID. I knew straight away that this was probably related to me using Zaphod mode and a test with a single screen did indeed make the problem go away. There was still the occasional flicker though, which may or may not be related. I don't get any flickering with the code removed (see attached patch) while using Zaphod mode.
I knew it was probably related to Zaphod mode because I know that the CRTCs play a key role there but beyond that, I'm not sure what the problem is. I don't know exactly what this code is used for.
I probably should have tested two screens without Zaphod mode but my wife will kill me if I restart the machine again. ;) I'm guessing that isn't affected because it's a very common setup.