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Old 07-06-2011, 07:54 PM
Tim Gardner
 
Default Need some kernel help...

On 07/06/2011 01:45 PM, Scott Bambrough wrote:

Hi guys,

I did an upgrade from Maverick to Natty on the weekend and ran into a
glitch with HDMI video display. I filed the following bug if you are
interested:

https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-intel/+bug/805416

I think it is a kernel issue, related to bad EDID data being returned to
the DRM subsystem. In particular I think the problem is caused by HDMI
audio being enabled.

I was looking through the Intel i915 driver to see if I can disable
audio easily. It looks like there is a way to disable it via a
kernel/module command line option, but I can't seem to figure out how or
what to set. Is there anyone in your group who might be able to point
me in the right direction?

Scott



Forwarding to the kernel-team@lists.ubuntu.com list...

--
Tim Gardner tim.gardner@canonical.com

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Old 07-07-2011, 01:39 PM
Seth Forshee
 
Default Need some kernel help...

On Wed, Jul 06, 2011 at 01:54:16PM -0600, Tim Gardner wrote:
> On 07/06/2011 01:45 PM, Scott Bambrough wrote:
> >Hi guys,
> >
> >I did an upgrade from Maverick to Natty on the weekend and ran into a
> >glitch with HDMI video display. I filed the following bug if you are
> >interested:
> >
> >https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-intel/+bug/805416
> >
> >I think it is a kernel issue, related to bad EDID data being returned to
> >the DRM subsystem. In particular I think the problem is caused by HDMI
> >audio being enabled.

Can you explain what is leading you to conclude that this is due to a
bad EDID and/or HDMI audio? I'm not all that knowledgable in this area,
but at a glance I don't see anything on the bug that indicates an
invalid EDID -- the kernel isn't screaming about bad checksums, and the
monitor data in Xorg.log looks sane.

> >I was looking through the Intel i915 driver to see if I can disable
> >audio easily. It looks like there is a way to disable it via a
> >kernel/module command line option, but I can't seem to figure out how or
> >what to set. Is there anyone in your group who might be able to point
> >me in the right direction?

Are you referring to the force_audio property? That's the only thing I'm
seeing that looks related. But it looks like the purpose of that is to
force HDMI audio to be enabled regardless of what's in the EDID.

Seth

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Old 07-07-2011, 01:39 PM
Seth Forshee
 
Default Need some kernel help...

On Wed, Jul 06, 2011 at 01:54:16PM -0600, Tim Gardner wrote:
> On 07/06/2011 01:45 PM, Scott Bambrough wrote:
> >Hi guys,
> >
> >I did an upgrade from Maverick to Natty on the weekend and ran into a
> >glitch with HDMI video display. I filed the following bug if you are
> >interested:
> >
> >https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-intel/+bug/805416
> >
> >I think it is a kernel issue, related to bad EDID data being returned to
> >the DRM subsystem. In particular I think the problem is caused by HDMI
> >audio being enabled.

Can you explain what is leading you to conclude that this is due to a
bad EDID and/or HDMI audio? I'm not all that knowledgable in this area,
but at a glance I don't see anything on the bug that indicates an
invalid EDID -- the kernel isn't screaming about bad checksums, and the
monitor data in Xorg.log looks sane.

> >I was looking through the Intel i915 driver to see if I can disable
> >audio easily. It looks like there is a way to disable it via a
> >kernel/module command line option, but I can't seem to figure out how or
> >what to set. Is there anyone in your group who might be able to point
> >me in the right direction?

Are you referring to the force_audio property? That's the only thing I'm
seeing that looks related. But it looks like the purpose of that is to
force HDMI audio to be enabled regardless of what's in the EDID.

Seth

--
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Old 07-08-2011, 07:29 PM
Scott Bambrough
 
Default Need some kernel help...

On Thu, 2011-07-07 at 08:39 -0500, Seth Forshee wrote:
> On Wed, Jul 06, 2011 at 01:54:16PM -0600, Tim Gardner wrote:
> > On 07/06/2011 01:45 PM, Scott Bambrough wrote:
> > >Hi guys,
> > >
> > >I did an upgrade from Maverick to Natty on the weekend and ran into a
> > >glitch with HDMI video display. I filed the following bug if you are
> > >interested:
> > >
> > >https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-intel/+bug/805416
> > >
> > >I think it is a kernel issue, related to bad EDID data being returned to
> > >the DRM subsystem. In particular I think the problem is caused by HDMI
> > >audio being enabled.
>
> Can you explain what is leading you to conclude that this is due to a
> bad EDID and/or HDMI audio? I'm not all that knowledgable in this area,
> but at a glance I don't see anything on the bug that indicates an
> invalid EDID -- the kernel isn't screaming about bad checksums, and the
> monitor data in Xorg.log looks sane.

This post leads me to believe the problem is HDMI audio is enabled.
http://lists.freedesktop.org/archives/intel-gfx/2010-October/008321.html

See the picture in the bug.

> > >I was looking through the Intel i915 driver to see if I can disable
> > >audio easily. It looks like there is a way to disable it via a
> > >kernel/module command line option, but I can't seem to figure out how or
> > >what to set. Is there anyone in your group who might be able to point
> > >me in the right direction?
>
> Are you referring to the force_audio property? That's the only thing I'm
> seeing that looks related. But it looks like the purpose of that is to
> force HDMI audio to be enabled regardless of what's in the EDID.

Yes that was the property I was looking at.

Scott

--
Scott Bambrough <scott.bambrough@linaro.org>
Technical Director, Linaro Landing Teams


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Old 07-08-2011, 08:24 PM
Seth Forshee
 
Default Need some kernel help...

On Fri, Jul 08, 2011 at 03:29:21PM -0400, Scott Bambrough wrote:
> On Thu, 2011-07-07 at 08:39 -0500, Seth Forshee wrote:
> > On Wed, Jul 06, 2011 at 01:54:16PM -0600, Tim Gardner wrote:
> > > On 07/06/2011 01:45 PM, Scott Bambrough wrote:
> > > >Hi guys,
> > > >
> > > >I did an upgrade from Maverick to Natty on the weekend and ran into a
> > > >glitch with HDMI video display. I filed the following bug if you are
> > > >interested:
> > > >
> > > >https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-intel/+bug/805416
> > > >
> > > >I think it is a kernel issue, related to bad EDID data being returned to
> > > >the DRM subsystem. In particular I think the problem is caused by HDMI
> > > >audio being enabled.
> >
> > Can you explain what is leading you to conclude that this is due to a
> > bad EDID and/or HDMI audio? I'm not all that knowledgable in this area,
> > but at a glance I don't see anything on the bug that indicates an
> > invalid EDID -- the kernel isn't screaming about bad checksums, and the
> > monitor data in Xorg.log looks sane.
>
> This post leads me to believe the problem is HDMI audio is enabled.
> http://lists.freedesktop.org/archives/intel-gfx/2010-October/008321.html
>
> See the picture in the bug.

I see. The HDMI audio problem referred to in that thread seems to have
been fixed for some time (commit 2e3d6006 merged in 2.6.37-rc1). Later
the force_audio property was added to allow the user to enable audio
regardless of what's in the EDID. So unless you somehow have this
property enabled, whether or not HDMI audio is turned on should depend
on the EDID from you monitor.

Note that force_audio is a property of the connector in the DRM
subsystem, not a command line prameter. It looks like they are set and
queried via ioctl, but I'm not sure whether there's any easy way to
check the value from userspace. You can see whether the
SDVO_AUDIO_ENABLE bit is set running intel_audio_dump (from the
intel-gpu-tools package). SDVO_AUDIO_ENABLE is bit 6 of SDVO[BC].

Seth

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