On Mon, Apr 15, 2013 at 10:49 PM, Chris Wilson <chris at chris-wilson.co.uk> wrote: > On Mon, Apr 15, 2013 at 06:59:58PM +0200, Daniel Vetter wrote: >> On Mon, Apr 15, 2013 at 6:38 PM, Jani Nikula <jani.nikula at intel.com> wrote: >> > On Mon, 15 Apr 2013, Chris Wilson <chris at chris-wilson.co.uk> wrote: >> >> On Fri, Apr 12, 2013 at 03:18:37PM +0300, Jani Nikula wrote: >> >>> Backlight data and registers are fiddled through LVDS/eDP modeset >> >>> enable/disable hooks, backlight sysfs files, asle interrupts, and register >> >>> save/restore. Protect the backlight related registers and driver private >> >>> fields using a spinlock. >> >>> >> >>> The locking in register save/restore covers a little more than is strictly >> >>> necessary, including non-modeset case, for simplicity. >> >>> >> >>> v2: Cover register access, save/restore, i915_read_blc_pwm_ctl() and code >> >>> paths leading there. >> >>> >> >>> Signed-off-by: Jani Nikula <jani.nikula at intel.com> >> >> >> >> Looks reasonable. >> >> >> >> intel_panel_actually_set_backlight() should have a WARN_ON(!spinlocked); >> >> >> >> The irqness of the register writes scares me slightly - since the IRQ in >> >> question is from ACPI and we have a few bug reports along the lines of >> >> "backlight makes the entire system sluggish" i.e. commonly associated >> >> with bad interrupt handling. Whilst you are looking at updating the >> >> backlight programming, can you look at pushing the writes from out >> >> of the interrupt handler? >> > >> > So, add a work to do the register writes, and change the spinlock into a >> > mutex while at it? Should be fairly simple, if you think that's the way >> > to go. >> >> I think I'll go ahead with the spinlock fix here for 3.10 and we can >> look into offloading this all for 3.11. Also, Chris do you remember >> one of these reports - I've kinda never noticed that particular kind >> of suck? > > I maybe way off the mark and the cause is likely just to be a sucky ACPI > firmware: > https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-intel/+bug/1019370 > > spinlock -> mutex + workqueue would mitigate against any bad firmware > being run under irq context. Hm, that's a funny one indeed. Although it's strange that it doesn't happen when not using X. Might be that the user doesn't notice it (since all the interactive stuff - blinking cursor - is done in irq context), but if this is indeed ACPI doing something crazy I have no idea what's it doing ... -Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch
