[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 #21 from Jani Nikula <jani.nikula at intel.com> ---
(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.

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.

(Of course, there are also machines where the firmware messes with the
backlight registers directly also. I don't know how to distinguish those.)

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