[Intel-gfx] [PATCH 2/4] drm/i915: protect backlight registers and data with a spinlock

[Daniel Vetter]

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?
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch