[Bug 81711] [855gm] Thinkpad R51 reports [drm:i9xx_set_fifo_underrun_reporting] *ERROR* pipe A underrun

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=81711

--- Comment #20 from Jean Delvare <jdelvare at suse.de> ---
I bisected this issue and here are my results.

First of all, there are two sets of error messages to consider: the one from
i9xx_set_fifo_underrun_reporting, and the rest.

The error message from i9xx_set_fifo_underrun_reporting appeared with commit
e69abff0d6794311d834de0fa2f188eb24a977b9 ("drm/i915: Check for FIFO underuns
when disabling reporting on gmch platforms" in v3.16.) This commit is merely
adding detection and reporting of the error condition, so this is not a
regression per se.

The other messages appeared with commit
fc2c807b7a2b2ca8dbe2aed2f5ae730c19beeda5 ("drm/i915: Make underruns DRM_ERROR"
in v3.15.) Again this commit is only making the reporting of the error
conditions unconditional, so this is not a regression per se.

As a summary, the underruns have always been there, just they were not reported
as errors before.

Can someone please explain how bad these pipe underruns are? And if/how they
can be fixed?

I admit I find it strange that messages that were reported at debug level
before were suddenly considered so important that they needed to be reported at
error level. I understand that driver developers would like to see these
messages without having to turn debugging on, but may I suggest that info level
would seem more appropriate?

The reason why I am suggesting that is that these early error messages kill the
nice splash screen at boot time. Info messages would not.

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