[Bug 105604] [CI][KBL only] igt@* - dmesg-warn - *ERROR* CPU pipe [A|B] FIFO underrun

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=105604

--- Comment #8 from Mun, Gwan-gyeong <elongbug at gmail.com> ---
After investigating the issue, I am suspecting a GEN9 hardware issue.
I figured out enabling FBC on a plane which has a combination of a 180-degree
rotation with having a Height that isn't divisible by 4 occasionally causes
FIFO underrun.
I tested the issue with igt-gpu-tools. ( multiplane-rotation-cropping-top
subtest from kms_rotation_crc).
I tested on Gen9 disaply HWs (both Skylake and Kabylake).
when I added the patch code which make avoiding the issue case, I could always
passed the test case.
https://gitlab.freedesktop.org/elongbug/drm-tip/tree/gen9_fbc_underrun01
https://gitlab.freedesktop.org/elongbug/drm-tip/commit/a3969a959230153a53088a0abbf354c4c233af20

I asked a HW guy this issue to clarify.
And for now I am waiting the reply.

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