GPU/DRM issue with DSI commands on msm 8916

[Daniel Mack]

Hi,

I'm having issues with the GPU/DRM drivers on a msm8916 based platform
which is very similar to the DragonBoard 410c. In my setup, a DSI
display is directly connected to the SoC, and the video link is stable.

However, when the host sends DCS commands down to the DSI panel (for
instance to set the backlight brightness), the image drops out, most of
the time only in terms of a short flicker, but sometimes it will
completely kill the image. In the latter case, only restarting the
Wayland compositor in userspace helps. This is also quite reproducible;
sending a NOP command once a second would give a visual flicker in 90%
of the cases, and it needs at most a minute to make the screen turn black.

The interesting thing is that this used to work in a v4.9 based version,
but it broke somewhere on the way to v4.14. Unfortunately, the platform
does not boot a vanilla kernel, so I can't really bisect this. We
currently depend on the Linaro downstream patches which can be found here:


http://git.linaro.org/landing-teams/working/qualcomm/kernel.git/log/?h=release/qcomlt-4.9

http://git.linaro.org/landing-teams/working/qualcomm/kernel.git/log/?h=release/qcomlt-4.14

I've looked at the development that has happened in the area for some
time now, but I can't really pin-point any specific commit. Also, I
cherry-picked most of the patches to these drivers that came in after
v4.14, but that didn't help either.

Has this has been observed before? A pointer what to investigate on
would be very much appreciated. If there is any more information I can
provide, please let me know.


Thanks,
Daniel