[Bug 101245] Haswell ULT max. resolution regression in KMS [HSW] [i915]

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=101245

Ville Syrjala <ville.syrjala at linux.intel.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |NEEDINFO

--- Comment #9 from Ville Syrjala <ville.syrjala at linux.intel.com> ---
(In reply to Michael Mounteney from comment #8)
> > "Apparently HDMI->DVI dual mode adapter where we aren't able to infer the capabilities of the sink, and limit the clock rate to what we know works."
> It did work up to 4.8.17.  I am using an Intel NUC with mini-HDMI to HDMI. 
> No DVI-anything involved.

[    2.488338] [drm:gmbus_xfer [i915]] GMBUS [i915 gmbus dpb] NAK for addr:
0040 w(1)

Means there is no DP++ dongle involved.

[   11.111354] [drm:drm_add_edid_modes [drm]] HDMI: DVI dual 1, max TMDS clock
250000 kHz

This means the display itself is telling us that its max TMDS clock is lower
than clock required by the 4k and 25x16 modes. The fact that it's saying dual
link DVI and max TMDS clock > 165MHz in the same sentence is also a bit
nonsensical since that exceeds the DVI spec, and dual link HDMI doesn't
actually exist.

I suppose we were ignoring the limits declared by the sink before I added the
DP dual mode stuff, and hence we allowed the out of spec modes through.

> 
> > "It should be possible to work around this by adding user modes with xranrd."
> As per my original description, xrandr user modes do not work.

You should use the same mode as the EDID has instead of trying CVT. The EDID
seems to have something like this:
"2560x1600" 268.5 2560 2608 2640 2720 1600 1603 1609 1646 +hsync +vsync

which seems to be almost the same as what 'cvt -r' would give you apart from
the vsync polarity.

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