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

[Takashi Iwai]

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?


Takashi