Curious experiences with a Radeon on the fritz

[Alex Deucher]

On Mon, Sep 12, 2011 at 2:13 PM, Michael Witten <mfwitten at gmail.com> wrote:
> I hope you find this adventure interesting, and I hope you
> provide me with some insight.
>
> Recently, I booted my computer, a Dell Latitude D810 that has a
> Radeon Mobility x600 (R300); all systems were waking up as normal:
>
>  * The Dell logo popped up in some ancient VGA mode.
>  * The GRUB menu appeared for 3 seconds as instructed.
>  * Linux loaded and started spewing out log messages.
>
> and then:
>
>    BAM!
>
> At around:
>
>  2011-09-09 20:27:07 +0000
>
> the Darkness overcame me; my laptop's LCD panel went black with nary
> a sign of life. After poking around a bit via ssh, I couldn't figure
> out what was going on; I had been running all the relevant code
> without trouble for some time now, so it just didn't make sense, and
> I began suspecting hardware failure.
>
> I strolled on over to freenode/#radeon, where I explained that I was
> still getting graphics at early boot time, but that it was dying
> shortly after Linux loaded. A one named Tari suggested that I boot
> with `nomodeset' in order to avoid anything more complicated than
> the standards of the Ancients.
>
> And Lo! With that very kernel command line parameter, the boot
> process did indeed land me safely in a working, albeit cramped
> VGA-backed virtual console.
>
> Searching the logs a bit more revealed the following:
>
>  [drm:drm_calc_timestamping_constants] *ERROR* crtc 10: Can't
>  calculate constants, dotclock = 0!
>
> Then (skipping a few interesting adventures), I ultimately discovered
> this kernel message:
>
>  [drm] Panel Size 1920x4095
>
> which is curious indeed!, because my laptop's panel size should be
> `1920x1200'. I booted into the computer's BIOS only to find that
> it too was being fooled into thinking that the display dimensions
> are `1920x4095'.
>
> Why might this have happened? Are bits stuck? Did something get fried?

Looks like your bios got corrupted somehow.  All of the vertical
timing in your panel modeline is bogus.  You'll need to patch up all
the vertical timing values the same way you patched up the vdisplay in
radeon_combios.c.  You'll have to try and find the native mode timing
for your panel.  Note that other data that the driver uses from the
vbios may also be corrupt.

The xserver defaults to 96dpi because there are too many broken EDIDs
out there and no good way to deal with different DPIs across different
monitors in multi-head desktops.  Also, a lot of users expect 96 dpi
and file bugs when it's something else.

Alex