[Bugme-janitors] [Bug 23472] 2.6.37-rc2 vs. 2.6.36 laptop backlight changes?

bugzilla-daemon at bugzilla.kernel.org bugzilla-daemon at bugzilla.kernel.org
Wed Nov 24 06:01:23 PST 2010


https://bugzilla.kernel.org/show_bug.cgi?id=23472





--- Comment #13 from Patrick Schaaf <kernelorg at bof.de>  2010-11-24 14:01:22 ---
(In reply to comment #11)

> It's odd that you have to write the 6 out before you can write the 7.  That
> used to be the way it worked in 2008 but in Jan 2009 they changed it to always
> write the setting even if it was the same as the current brightness.

It tries to...

I instrumented dell-laptop.c:dell_send_request, to show me the brightness
setting and getting activity.

I can see then, that when echoing to the sys knobs, the request is passed on,
even when the apparent value does not change.

In my test case, switchint between the GDM login screen and the text console, I
do NOT see any calls to that dell_send_request - I.E. THE DIMMING DOES NOT
HAPPEN THROUGH THE BRIGHTNESS API.

When on the text console, echoing 7 to the brightness sysfs file, I DO see
dell_send_request being called with the expected parameters, but it has no
visible effect on the dimness.

The dell_send_request function calls dcdbas.c:dcdbas_smi_request, which in turn
and pretty much unconditionally, makes an "outb" SMI request. That
dcdbas_smi_request function has a single other caller, in the dcdbas.c module,
which I also instrumented, just to find that path to be never called. So the
DIMMING DOES NOT HAPPEN THROUGH THE dcdbas SMI API, as far as I an see.

It appears as if the dimming is a side effect of something else (mode
switching?) on this platform, and it appears as if the SMI handler of the
laptop itself remembers what was set "officially" the last time.

Any idea what to look at, next?


I also instrumented

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