[Intel-gfx] [PATCH] drm/edid: Adding common CVT inferred modes when monitor allows range limited ones trough EDID.

[Alex Deucher]

On Fri, Apr 13, 2012 at 11:41 AM, Takashi Iwai <tiwai at suse.de> wrote:
> At Fri, 13 Apr 2012 11:30:01 -0400,
> Alex Deucher wrote:
>>
>> On Fri, Apr 13, 2012 at 11:13 AM, Takashi Iwai <tiwai at suse.de> wrote:
>> > At Fri, 13 Apr 2012 15:35:04 +0100,
>> > Dave Airlie wrote:
>> >>
>> >> > I don't think we need to support all wild modes, too.  But the _very_
>> >> > common modes like 1366x768 and 1600x900 should be really supported as
>> >> > default.
>> >>
>> >> You guys still haven't answered the basic question, what HW is this broken?
>> >
>> > The reported problem is about HP laptops with i915 driver (no matter
>> > chip chip is) and several monitors with resolutions more than the
>> > laptop panel.
>> >
>> > The LVDS provides only the native resolution (either 1366x768 or
>> > 1600x900) and a few other VESA ones (1024x768, 800x600 and 640x480).
>> > Meanwhile, the monitor EDID doesn't provide such laptop-native
>> > resolutions.
>> > Thus, in clone mode, the only possible resolution is 1024x768 or
>> > lower.  That's the whole problem.  It's too low and doesn't match with
>> > 16:9 although both laptop and monitor panels are 16:9.
>> >
>> > HP wants the clone mode of the laptop-native resolution and/or a
>> > higher resolution with the right aspect ratio like 1280x720.  Neither
>> > work as of now unless you add the extra mode manually.
>> >
>>
>> One thing to be careful of is that some monitors (especially LCD
>> panels) don't like modes that are not in their EDIDs.  As such when
>> you try and set them you often get a wonky display or more often a
>> blank screen.  We used to add a lot of inferred modes to the mode list
>> in the xserver which resulted in a lot of blank screens when some odd
>> mode was picked as the best match for a cloned display.  The "fix" was
>> to only add the inferred modes on analog monitors which were more
>> likely to be able to support them.
>
> Thanks, it's good to know!
>
> Though, I still wonder whether adding inferred modes for 1366x768 or
> 1600x900 would cause any big problems.  On such monitors, 1360x768 or
> 1440x900 (or 1680x1050) are usually seen in the supported list.
>
> Of course, it's never 100% safe.  But not so bad odds?

Probably ok on recent LCD panels as long as rb cvt modes are mostly
used.  Just something to keep in mind.

Alex