[Bug 82634] [snb] backlight issue on TOSHIBA PORTEGE R830 after suspend/resume

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=82634

--- Comment #22 from Hans de Goede <jwrdegoede at fedoraproject.org> ---
Hi,

(In reply to Jani Nikula from comment #21)
> (In reply to Hans de Goede from comment #19)
> > Also having 2 pieces of code (the i915 driver and the firmware) poling at
> > the same registers during suspend / resume is just wrong, that it happens to
> > often work does not make it less wrong, we really should always be loading
> > either the i915 or the acpi-video backlight driver and not both.
> 
> Depending on the machine, the firmware might actually ask i915 to adjust the
> brightness through the ACPI opregion. So only one entity actually touches
> the backlight registers, with locks held, but there are two interfaces for
> it.

Ah I did not know that, that is good to know. Given the test results it looks
like you're right and my patch is a bad idea.

> This appears to be the case here too, and your patch disables the ACPI
> interface as well. One could try disabling just the registering of the
> intel_backlight sysfs interface.

I deliberately disabled all of it and not just the sysfs interface, AFAICT
nothing should touch the sysfs interface if the acpi_video0 interface is
registered, as both the intel ddx and gnome will prefer acpi_video0 over the
intel interface.

Sylvain, do you still have an xorg.conf file hanging around telling the intel
ddx to use the intel_backlight interface? Can you try running the latest
Fedora-22 kernel without such a file and without any special kernel commandline
arguments? If that does not help then I'm afraid I'm all out of ideas and one
of the intel devs will need to look at reg-dumps and figure out what exactly is
going on at a much lower level.

If we need to get one of the Intel devs to look into the reg-dumps it would be
good if you could provide new register dumps from both pre and post resume with
the latest F-22 kernel without any special kernel commandline args.

Regards,

Hans

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