Discussion:
kernel-desktop-3.15.8-2.1.g258e3b0.x86_64 - Horrible Backlight Flicker (3.15.6 OK)
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David C. Rankin
2014-08-08 14:24:57 UTC
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All,

I have the Kernel:/stable/standard/ repo configured (bug testing on backlight
control) and today I pulled in the updated kernel:

kernel-desktop-3.15.8-2.1.g258e3b0.x86_64

Every 1-2 seconds the backlight flickers horribly (not related to bug report
of backlight keyboard keys not controlling backlight). It makes the laptop unusable.

I booted back into kernel-desktop-3.15.6-2.1.gedc5ddf.x86_64 and all is fine.
Does a bug report need to go somewhere? I know this is from
Kernel:/stable/standard/, but if this is getting folded into factory, then a bug
needs to go somewhere.

Anybody have anything to check? The flicker starts as soon as the kernel is
booted, is present during the splash screen and remain unchanged after the
display and window managers load -- so it is kernel/module related and not
desktop related...

This is on a Toshiba p205d [AMD/ATI] RS690M [Radeon Xpress 1200/1250/1270]. I
have never seen backlight flicker before on this laptop and dropping back to
3.15.6 all is fine.
--
David C. Rankin, J.D.,P.E.
Takashi Iwai
2014-08-08 15:18:06 UTC
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At Fri, 08 Aug 2014 09:24:57 -0500,
Post by David C. Rankin
All,
I have the Kernel:/stable/standard/ repo configured (bug testing on backlight
kernel-desktop-3.15.8-2.1.g258e3b0.x86_64
Every 1-2 seconds the backlight flickers horribly (not related to bug report
of backlight keyboard keys not controlling backlight). It makes the laptop unusable.
I booted back into kernel-desktop-3.15.6-2.1.gedc5ddf.x86_64 and all is fine.
Does a bug report need to go somewhere? I know this is from
Kernel:/stable/standard/, but if this is getting folded into factory, then a bug
needs to go somewhere.
Anybody have anything to check? The flicker starts as soon as the kernel is
booted, is present during the splash screen and remain unchanged after the
display and window managers load -- so it is kernel/module related and not
desktop related...
This is on a Toshiba p205d [AMD/ATI] RS690M [Radeon Xpress 1200/1250/1270]. I
have never seen backlight flicker before on this laptop and dropping back to
3.15.6 all is fine.
Such a bug is better reported to upstream, e.g. bugzilla.kernel.org.

Through a quick look at commits between 3.15.6 and 3.15.8, the
suspicious one is the fix
be907c8468c9f47882036109ba550cd2748b86a0
drm/radeon: set default bl level to something reasonable

You may try to revert this commit. If this doesn't help, you'd need
to check via git bisect, at best. In anyway, be prepared to build a
kernel by yourself :)


Takashi

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