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

[Jani Nikula <jani.nikula@intel.com>]

On Mon, 15 Apr 2013, Chris Wilson <chris@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@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.

BR,
Jani.