XRandR EDID missed with Cedar on LVDS

Alex Deucher alexdeucher at gmail.com
Wed Nov 2 15:45:46 PDT 2011

On Wed, Nov 2, 2011 at 6:34 PM, Kai-Uwe Behrmann <ku.b at gmx.de> wrote:
> Am 02.11.11, 17:41 -0400 schrieb Alex Deucher:
>> On Wed, Nov 2, 2011 at 5:03 PM, Kai-Uwe Behrmann <ku.b at gmx.de> wrote:
>>> While testing a ATI Cedar equiped laptop I could not get the EDID for the
>>> interal LVDS in user space. I tried xrandr and xcmddc with no results.
>>> But
>>> the /var/log/Xorg.0.log showed that EDID was detected and hwinfo gives
>>> the
>>> monitor manufacturer. Still user space applications needs the complete
>>> data
>>> block to configure the monitor.
>> Can you post your xorg log and dmesg output?  There are several
>> possibilities:
> They are here:
> https://bugs.freedesktop.org/show_bug.cgi?id=32343#c7
>> 1. Your panel does not provide an EDID.  The driver is still able to
>> determine the native mode timings from tables in the vbios.
> This LVDS' EDID looks like being detected by frglx. It might be broken.
> On the other side xcmddc shows an external monitors EDID but does not listen
> the this LVDS one. xcmddc uses i2c communication. Not sure what frglx does
> to see the discussed LVDS EDID.

We may need a machine specific quirk for your laptop, or it's possible
the closed driver is generating a fake edid using the modeline and
vendor info from the vbios tables.  Please attach your vbios to the
bug above and I'll see what I can find out.


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