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Old 03-17-2010, 01:12 AM
Scott James Remnant
 
Default Debugging KMS (and thoughts thereof)

On Tue, 2010-03-16 at 18:44 -0700, Bryce Harrington wrote:

> As we move into the new world of KMS, I'm noticing that a lot of our
> established procedures and tools for debugging modesetting problems no
> longer work.
>
One thing I did notice from talking with upstream nouveau today and
debugging the Latitude D620 - our kernels don't have mmiotrace support
compiled in.

I'm not sure why, perhaps kernel team could answer that?

It looks like a tracer like any other, and has to be enabled through
sysfs before it actually traces - surely this would be a good thing to
have?

That then turns all nouveau issues into "fire up nvidia-glx under
mmiotrace", "send upstream"

Scott
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Old 03-17-2010, 05:12 AM
Bryce Harrington
 
Default Debugging KMS (and thoughts thereof)

On Wed, Mar 17, 2010 at 02:12:04AM +0000, Scott James Remnant wrote:
> On Tue, 2010-03-16 at 18:44 -0700, Bryce Harrington wrote:
>
> > As we move into the new world of KMS, I'm noticing that a lot of our
> > established procedures and tools for debugging modesetting problems no
> > longer work.
> >
> One thing I did notice from talking with upstream nouveau today and
> debugging the Latitude D620 - our kernels don't have mmiotrace support
> compiled in.
>
> I'm not sure why, perhaps kernel team could answer that?
>
> It looks like a tracer like any other, and has to be enabled through
> sysfs before it actually traces - surely this would be a good thing to
> have?

Yeah RAOF and I discussed adding mmiotrace support in our debugging
tools. He didn't think it would buy us much. But I'll let him
explain his findings...

> That then turns all nouveau issues into "fire up nvidia-glx under
> mmiotrace", "send upstream"

Ha if only it were so simple. All our bugs would belong to them.

Bryce


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Old 03-17-2010, 06:49 AM
Geir Ove Myhr
 
Default Debugging KMS (and thoughts thereof)

On Wed, Mar 17, 2010 at 2:44 AM, Bryce Harrington <bryce@canonical.com> wrote:
> Resolution Selection Fallback Issues
> ------------------------------------
> Sometimes the issue is that some problem is causing the modesetting
> logic to fail to find a suitable resolution and it goes into various
> fallbacks. *These sometimes make unsatisfactory choices in the hope of
> picking a safe default. *Usually we can spot this going on by looking at
> the Xorg.0.log, where it prints out information about each resolution
> it's considering and what timings it sees, and why it didn't pick it.
>
> This same thing must be going on in the kernel, but I don't see anything
> in dmesg or syslog about it, and I don't see much in the way of printk's
> in the edid drm code. *You may find it useful to add some verbosity in
> here so that there's more details in log files about why it is not
> picking resolutions.

I still see resolution picking in Xorg.0.log, even with KMS, at least
on intel. In order to make the kernel more verbose about what it's
doing, the kernel option drm.debug=0x04 can be used. It will enable
the macro DRM_DEBUG_KMS which should tell what is going on both for
resolution picking and output detection. The drm debug levels are
defined in include/drm/drmP.h [1]. I think I have also seen upstream
asking for Option ModeDebug in xorg.conf again, which used to be more
verbose about the modesetting in UMS, so possibly they have made this
work with KMS as well now, but I haven't tested this (again, this is
on intel graphics).

[1]: http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=include/drm/drmP.h;h=4a3c4e441027be39da3d37b8a817ff9f918661dd; hb=HEAD

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Old 03-17-2010, 11:20 AM
Andy Whitcroft
 
Default Debugging KMS (and thoughts thereof)

On Wed, Mar 17, 2010 at 02:12:04AM +0000, Scott James Remnant wrote:
> On Tue, 2010-03-16 at 18:44 -0700, Bryce Harrington wrote:
>
> > As we move into the new world of KMS, I'm noticing that a lot of our
> > established procedures and tools for debugging modesetting problems no
> > longer work.
> >
> One thing I did notice from talking with upstream nouveau today and
> debugging the Latitude D620 - our kernels don't have mmiotrace support
> compiled in.
>
> I'm not sure why, perhaps kernel team could answer that?

This seems to be an oversight. Looking at the option it seems
completely safe to turn on performance wise if its of use in debugging.
Patches to do this are out on the kernel-team list for review.

> It looks like a tracer like any other, and has to be enabled through
> sysfs before it actually traces - surely this would be a good thing to
> have?
>
> That then turns all nouveau issues into "fire up nvidia-glx under
> mmiotrace", "send upstream"

-apw

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