On Sun, Oct 14, 2018 at 05:12:00PM +0200, Hans de Goede wrote: > Hi All, > > Here are 2 more / new pwm-lpss fixes. > > I've received a bug report that the recent ACPI-LPSS code changes which > properly order device resume on Cherry Trail so that the GFX0 _PS0 method > no longer exits with an error causes the backlight to flicker on some > Cherry Trail devices. > > This series is the result of investigating this issue. On Cherry Trail > devices under Windows the PWM controller used for the backlight is > considered part of the GPU even though it is part of the LPSS block and > thus is an entirely different independent hardware unit. > > Because of this on Cherry Trail the GPU's (GFX0 ACPI node) _PS3 and _PS0 > ACPI methods save and restore the PWM controller registers. > > After the recent fixes this save + restore of the PWM controller registers > is actually also happening under Linux. > > If userspace blanks the screen before suspending, such as e.g. GNOME > does, then the PWM controller will be runtime-suspended when the suspend > starts. This causes the GFX0 _PS3 method to save a value of 0xffffffff > for the PWM control register and to restore this value on resume. > Note that the GPU's _PS0 method also puts the PWM controller in D0, so > this write of 0xffffffff does actually stick. > > The first patch in this patch-set fixes this. This fix exposes another > issue, the pwm-lpss driver unconditionally sets the update bit when > pwm_apply gets called, even if nothing has changed. At least on > Cherry Trail this seems to cause the next update (which actually changes > something) to be ignored. The second patch fixes this issue. Applied, thanks. Thierry
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