XRandR EDID missed with Cedar on LVDS

Kai-Uwe Behrmann ku.b at gmx.de
Wed Nov 2 15:34:11 PDT 2011

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:

> 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.

> 2. Your EDID has a bad checksum/etc. and the kernel drm EDID validator
> rejects it:
> https://bugs.freedesktop.org/show_bug.cgi?id=31943
> You can try the patch on that bug and see if it helps.

kind regards

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