[Bug 90128] Big monitor has blank display (HDMI or DVI) in any kernel since and including 3.13 (despite earlier fixes)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=90128

--- Comment #13 from Ville Syrjala <ville.syrjala at linux.intel.com> ---
So the main problem here is that the monitor has a broken EDID. Whether it's
really broken or just doesn't like how we're trying to do the EDID read for
some reason I can't say.
[    4.546886] i915 0000:00:02.0: HDMI-A-1: EDID is invalid:
[    4.546887]  [00] GOOD 00 ff ff ff ff ff ff 00 12 ed fa 00 00 00 00 00
[    4.546888]  [00] GOOD 28 15 01 03 a5 3c 22 78 22 6f b1 a7 55 4c 9e 25
[    4.546888]  [00] GOOD 0c 50 54 00 00 00 01 01 01 01 01 01 01 01 01 01
[    4.546889]  [00] GOOD 01 01 01 01 01 01 56 5e 00 a0 a0 a0 29 50 30 20
[    4.546889]  [00] GOOD 35 00 55 50 21 00 00 1a 00 00 00 fc 00 51 48 44
[    4.546889]  [00] GOOD 32 37 30 0a 20 20 20 20 20 20 00 00 00 fc 00 0a
[    4.546890]  [00] GOOD 20 20 20 20 20 20 20 20 20 20 20 20 00 00 00 fc
[    4.546890]  [00] GOOD 00 0a 20 20 20 20 20 20 20 20 20 20 20 20 01 89
[    4.546891]  [01] BAD  ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
[    4.546891]  [01] BAD  ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
[    4.546891]  [01] BAD  ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
[    4.546892]  [01] BAD  ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
[    4.546892]  [01] BAD  ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
[    4.546892]  [01] BAD  ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
[    4.546893]  [01] BAD  ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
[    4.546893]  [01] BAD  ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff

Thanks to that broken EDID the only mode we can extract from it is 2560x144 at 60,
which is too high for DVI, so we reject the mode. We can't tell whether the
monitor is DVI or HDMI without having the CEA/HDMI block in the EDID. Whether
it was supposed to be in that all 'ff' block I can't say.

In any case then userspace for some reason decides to try to use a 1360x768
mode which the monitor apparently doesn't like and instead just displays
garbage.

So the way you should be able to make this work is manually adding the correct
mode (assuming the monitor was previously happy with out of spec DVI signal,
but from the explanation I got the impression that that indeed was the case).

As for the EDID fail, you could perhaps try this patch just to make sure we
don't have some GMBUS bug in the code causing this problem:
diff --git a/drivers/gpu/drm/i915/intel_i2c.c
b/drivers/gpu/drm/i915/intel_i2c.c
index b6401e8f1bd6..8780f411afa9 100644
--- a/drivers/gpu/drm/i915/intel_i2c.c
+++ b/drivers/gpu/drm/i915/intel_i2c.c
@@ -665,7 +665,7 @@ int intel_setup_gmbus(struct drm_i915_private *dev_priv)
                bus->reg0 = pin | GMBUS_RATE_100KHZ;

                /* gmbus seems to be broken on i830 */
-               if (IS_I830(dev_priv))
+               if (1||IS_I830(dev_priv))
                        bus->force_bit = 1;

                intel_gpio_setup(bus, pin);

Or if you have a non-Intel GPU around you could perhaps try to see if you can
read the full EDID on that one.

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