You might want to try the latest drm-intel-nightly git branch from http://cgit.freedesktop.org/~danvet/drm-intel This has a few more tricks which helped on some similar platforsm to yours (and similar resume issues). And please always include a mailing list when reporting issues, since your dear maintainer might be on vacation (or simply swamped with other stuff). Cheers, Daniel On Fri, Feb 8, 2013 at 8:36 PM, Kamal Mostafa <kamal at canonical.com> wrote: > Hi Paulo and Daniel- > > I've been tracking Daniel's work on i915 backlight for quite some time > now, in particular to support the Dell XPS13 (Sandybridge-mobile, > CougarPoint PCH) in the Ubuntu kernels. > > Daniel's backlight fixes which landed in 3.6 did enable working > backlight controls on the XPS13, but it appears that this commit from > Paolo broke it again: > > a4f32fc drm/i915: don't forget the PCH backlight registers > > More specifically, the behavior on the XPS13 is this: > > With the current 3.8-rc6 i915 stack (including a4f32fc), this machine > gets both of: /sys/class/backlight/{acpi_video0,intel_backlight}. > Changes to acpi_video0/brightness don't have any effect on the > backlight, unless I first "echo 0 > intel_backlight/brightness", then > acpi_video0 works properly. If I stuff a low non-zero number into > intel_backlight/brightness, then the backlight pulsates and flickers > continuously. > > If I revert a4f32fc (or just omit the setting of BLM_PCH_PWM_ENABLE in > intel_panel_enable_backlight) then my backlight controls work fine: > acpi_video0/brightness works at boot, and intel_backlight/brightness no > longer induces the pulsate/flicker effect (or any effect at all). > > So... before I go shooting my mouth off on intel-gfx, I wonder if either > of you can shed any (back)light on the situation (sorry ;-). > > I don't really have any reason to think that this issue is specific to > CougarPoint PCH, but since the XPS13 is PCH_CPT this patch fixes it for > me, for instance: > > --- a/drivers/gpu/drm/i915/intel_panel.c > +++ b/drivers/gpu/drm/i915/intel_panel.c > @@ -347,7 +347,9 @@ void intel_panel_enable_backlight(struct drm_device *dev, > POSTING_READ(reg); > I915_WRITE(reg, tmp | BLM_PWM_ENABLE); > > - if (HAS_PCH_SPLIT(dev)) { > + /* Note setting BLM_PCH_PWM_ENABLE breaks backlight on > + * Dell XPS13 (sandybridge_m, CougarPoint PCH). */ > + if (HAS_PCH_SPLIT(dev) && !HAS_PCH_CPT(dev)) { > tmp = I915_READ(BLC_PWM_PCH_CTL1); > tmp |= BLM_PCH_PWM_ENABLE; > tmp &= ~BLM_PCH_OVERRIDE_ENABLE; > > > I don't know if switching this based on HAS_PCH_CPT() is really relevant > -- it just works for the Dell XPS. (And please forgive my obvious > cluelessness about what PCH_CPT even means!) > > Any advice? > > -Kamal -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch
