Mode Setting through libdrm

Mode Setting through libdrm

[Alberto Simón Francés]

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Hello,

I have a question with regards to the libdrm library. I'm currently working
on an app that relies on KMS, DRM and EGL to output accelerated graphics
without a display server in between. It does so to reduce input latency.
The system this app will run is connected to a CRT monitor and I'd like to
be able to switch resolutions in order to use the best resolution depending
on the input of the user and do so as fast as possible. I understand that
this might pose problems to the user but it will run on a custom
installation of Linux devoted just to this application. It doesn't need to
interact with other apps at all.

The problem I have is that I haven't found info on how I would go about
doing this with libdrm. I need to be able to set custom timings to drive
the display, since it's not just about driving the monitor with standard
resolutions. This monitor doesn't report correct EDID info and won't report
it either. Currently it's using a single default resolution I baked in, but
the idea is to be able to switch between them.

I know that this is possible by drivers, I've seen examples in the drivers
themselves, but I still haven't been able to make the connection since the
documentation on the specific calls, functions and structures is sparse.

I'd appreciate any help you could give me or any pointers.

Best regards,
Alberto

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Re: Mode Setting through libdrm

[Ville Syrjälä]

On Wed, Mar 09, 2016 at 10:15:17AM -0300, Alberto Simón Francés wrote:
> Hello,
> 
> I have a question with regards to the libdrm library. I'm currently working
> on an app that relies on KMS, DRM and EGL to output accelerated graphics
> without a display server in between. It does so to reduce input latency.
> The system this app will run is connected to a CRT monitor and I'd like to
> be able to switch resolutions in order to use the best resolution depending
> on the input of the user and do so as fast as possible. I understand that
> this might pose problems to the user but it will run on a custom
> installation of Linux devoted just to this application. It doesn't need to
> interact with other apps at all.
> 
> The problem I have is that I haven't found info on how I would go about
> doing this with libdrm. I need to be able to set custom timings to drive
> the display, since it's not just about driving the monitor with standard
> resolutions. This monitor doesn't report correct EDID info and won't report
> it either. Currently it's using a single default resolution I baked in, but
> the idea is to be able to switch between them.
> 
> I know that this is possible by drivers, I've seen examples in the drivers
> themselves, but I still haven't been able to make the connection since the
> documentation on the specific calls, functions and structures is sparse.
> 
> I'd appreciate any help you could give me or any pointers.

Just populate a drmModeModeInfo with whatever custom timings you want,
and then feed it to drmModeSetCrtc().

-- 
Ville Syrjälä
Intel OTC
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