[Bug 105267] Screen flickering after getting hpd irq

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=105267

--- Comment #19 from Perry Yuan <perry_yuan at dell.com> ---
(In reply to Jani Nikula from comment #15)
> Thanks for testing.
> 
> The problem with the patch referenced in comment #10 is that will regress
> older platforms. We can't do that.
> 
> The background is that we have tried to use optimal link parameters, and we
> have tried to optimize for both fewer lanes with higher rate, and more lanes
> with lower rate. All of this failed, until we learned that, uh, a certain
> other OS always used the maximum link parameters reported by the display.
> Apparently that was the only configuration that the panel/laptop vendors
> then ended up validating. We switched to using max link rate and lane count,
> which presumably correspond to the native resolution of the display anyway,
> and we haven't had issues with that approach until now.
> 
> Arguably all the displays should work with all the lane counts and rates
> they report, but sadly this appears not to be the case. In this bug, the
> display does not work with the maximum parameters it reports.
> 
> Apparently nobody has double checked the DDI buffer translation and voltage
> swing etc. parameters that I suggested in comment #5. :(
> 
> eDP 1.4 also adds two somewhat related features. Link rate select to support
> more intermediate rates between what's available for DP. DSC to support
> stream compression.
> 
> 1) Please attach /sys/kernel/debug/dri/0/i915_vbt. The VBT is supposed to
> contain the port specific maximums, but perhaps that's not being used.
> 
> 2) Please see that you have CONFIG_DRM_DP_AUX_CHARDEV=y, and try to use
> /dev/drm_dp_auxN node to hexdump the DPCD, and attach them.

Hi  Jani:
If the patch has regression effect，then what we can do to fix the issue ?


Perry

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