How to retrieve graphic card driver display mode in dual/multi-monitor setup?

Ping Cheng pinglinux at
Mon Feb 15 16:13:48 PST 2010

Hi Rémi,

Thank you for the suggestions.  Please see my comments in line.


On Sun, Feb 14, 2010 at 3:25 PM, Rémi Cardona <remi at> wrote:
> Le 14/02/2010 22:36, Ping Cheng a écrit :
>> So, my questions are:
>> 1.  What is the proper way to retrieve TwinView's display mode and
>> metamodes inside an (input) device driver?
> Short of parsing Xorg.0.log and/or xorg.conf to get to the nvidia stuff,
> I don't think that's doable with TwinView (since X is totally unaware of
> what the nvidia driver does, that's the whole idea behind TwinView...)

Accessing Xorg.0.log could be a solution.  I hoped there might be a
better way to handle this case. Since TwinView setting is pretty much
a static mode, we currently add TwinView related options to the
driver's fdi rules for hal/udev (linuxwacom.fdi) to make the options
"hot-pluggable". If there is no other way to go, we'll stay with .fdi
for TwinView.

>> 2.  What is the proper way to retrieve RandR display mode (extended,
>> clone, rotate...) and screen resolutions inside a device driver?  Is
>> there any difference in retrieving those info between RandR 1.2 and
>> 1.3?
> IMHO, that shouldn't be done in the driver, but in an external tool.
> That tool would query the server with XRandR to see which physical
> displays are available and then set the tablet's properties through XI2
> properties or what not.
> Peter will probably tell you something much clever, but I can't think of
> a compelling reason to do that at the driver level, when it can be done
> higher up in the stack, with better potential integration with input and
> display management tools in current desktop environments.

It is nice to know that you don't think the driver needs to worry
about this mapping feature.  In fact, I've already had a bash script
to handle the rotate and extended mode for RandR settings.  However, I
was suggested to embed the support into the driver.  That's why I had
this question here.  With your support, I might be able to convince
them that the feature is out of the driver's scope.

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