[PATCH] drm/radeon/kms: fix tv dac conflict resolver

GhePeU ghepeu at virgilio.it
Sat May 1 05:42:38 PDT 2010


Il giorno mar, 27/04/2010 alle 18.57 -0400, Alex Deucher ha scritto:
> On Tue, Apr 27, 2010 at 6:24 PM, GhePeU <ghepeu at virgilio.it> wrote:
> > Il giorno mar, 27/04/2010 alle 18.11 -0400, Alex Deucher ha scritto:
> >> On Tue, Apr 27, 2010 at 5:30 PM, GhePeU <ghepeu at virgilio.it> wrote:
> >> > Il giorno gio, 15/04/2010 alle 13.41 -0400, Alex Deucher ha scritto:
> >> >> >From 837feb147c531219c7315857a6f17e145af8f750 Mon Sep 17 00:00:00 2001
> >> >> From: Alex Deucher <alexdeucher at gmail.com>
> >> >> Date: Thu, 15 Apr 2010 13:31:12 -0400
> >> >> Subject: [PATCH] drm/radeon/kms: fix tv dac conflict resolver
> >> >
> >> > Hi,
> >> >
> >> > a few days ago I upgraded to the last 2.6.34 rc kernel and found that with
> >> > KMS both the console and X were using a 800x600 resolution instead of my LCD
> >> > display's native resolution of 1440x900 who was selected by default with
> >> > 2.6.33 and previous kernels.
> >> >
> >> > I tracked the problem to this patch, which causes the same issues also
> >> > when manually applied to 2.6.33: apparently the kms radeon driver
> >> > wrongly detects a TV connected to my card (I don't have one, only a LCD
> >> > display connected to the DVI port) and forces the TV default resolution
> >> > for all the outputs.
> >>
> >> You issue is not related to the patch.  What the patch does is allow
> >> you to use the digital part of DVI plus TV at the same time.  The
> >> analog part of the DVI port and the TV share the same DAC so they
> >> can't be used at the same time.  Prior to the patch, both the TV and
> >> DVI were detected as attached, but the TV was always disabled since it
> >> was wrongly seen as conflicting with the DVI.
> >>
> >> Your issue is actually a matter of load detection for TV not always
> >> being reliable.  I don't know what a proper fix would be.  We could
> >> disable load detection for TV to avoid false positives, but that would
> >> prevent automatic detection of TV which does work in most cases.
> >>
> >> Alex
> >>
> >
> > With UMS however I don't have this problem, is the logic different?
> >
> > Shouldn't the driver behavior with KMS be the same, in this case? At
> > least there wouldn't be (apparent) regressions like the one I'm
> > experiencing.
> >
> 
> UMS does not enable load detection on TV by default while KMS does,
> the difference being KMS provides both the console and X so you want
> to make sure you put something up on whatever monitors or tvs happen
> to be attached.  I'm not sure what the best answer is here.
> 
> Alex

Would it be possible to add a module option to disable tv load
detection? As things are now I must always change back the resolution to
1440x900 and disable the TV.

By the way I just tested "radeon.tv=0" and both 2.6.33 and 2.6.34 rc5
fail with a "BUG: unable to handle kernel NULL pointer dereference".
Syslog output attached.

Giacomo
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