[PATCH] drm: Add downclock quirk for Samsung LTN121AT10-301

[Sean Paul]

On Wed, May 30, 2012 at 1:06 AM, Rafał Miłecki <zajec5 at gmail.com> wrote:
> 2012/5/30 Sean Paul <seanpaul at chromium.org>:
>> On Tue, May 29, 2012 at 5:23 PM, Alex Deucher <alexdeucher at gmail.com> wrote:
>>> On Tue, May 29, 2012 at 4:33 PM, Sean Paul <seanpaul at chromium.org> wrote:
>>>> On Tue, May 29, 2012 at 10:43 AM, Alex Deucher <alexdeucher at gmail.com> wrote:
>>>>> On Mon, May 28, 2012 at 1:20 PM, Sean Paul <seanpaul at chromium.org> wrote:
>>>>>> On Wed, Jan 18, 2012 at 10:06 AM, Sean Paul <seanpaul at chromium.org> wrote:
>>>>>>> Add a quirk which adds a new downclocked mode to the EDID of Samsung
>>>>>>> LTN121AT10-301 panels. This allows the intel driver to apply downclocking
>>>>>>> and save power.
>>>>>>>
>>>>>>
>>>>>> Is there any feedback on the patch? I'd like to get it merged if possible.
>>>>>
>>>>> This seems like something that should be specific to the intel driver
>>>>> rather than risking problems with this monitor on other drivers.
>>>>>
>>>>
>>>> Thanks for the feedback, Alex. I had originally put this in the intel
>>>> driver, but moved it since it was a nasty hack. Furthermore, it was
>>>> less obvious that the mode was available, since it was hidden to all
>>>> layers above i915. The panel is just fine with the lower refresh rate,
>>>> so it shouldn't have any issues with other drivers.
>>>
>>> Well it doesn't really seem like a quirk per se, the monitor works
>>> just fine without it.  You are basically just adding an arbitrary new
>>> user defined mode that happens to work on the monitor.  Seems like you
>>> should just be adding the mode with xrandr or equivalent.
>>>
>>
>> Unfortunately, adding it via xrandr won't take advantage of the i915
>> lvds downclocking feature, which is the motivation for the patch.
>>
>> At any rate, it doesn't look like there's any interest in picking this
>> patch up, so we'll just carry it locally in chromium-os :(
>
> May I ask why? AFAIU you're just copying PREFERRED mode and changing
> it's clock. xrandr allows you to set custom clock, doesn't it?
>

Yes, definitely. The reason I can't set it via xrandr (easily) is
because we look for lvds downclock modes (in i915) on the driver init.
Since the driver initializes way before we have a chance to add a new
mode via xrandr, the driver won't have a downclock mode.

I suppose the other option is to hack the i915 driver to allow a
downclocked mode to be added after it's been initialized. I haven't
looked into this solution, it might be worth investigating.

Sean


> --
> Rafał