[Intel-gfx] [PATCH 1/8] drm/i915: Rebalance runtime pm vs forcewake

[Deepak S]

On Thursday 11 December 2014 03:45 PM, Chris Wilson wrote:
> On Fri, Dec 12, 2014 at 03:30:14PM +0530, Deepak S wrote:
>> On Monday 08 December 2014 11:57 PM, Mika Kuoppala wrote:
>>> From: Chris Wilson <chris at chris-wilson.co.uk>
>>>
>>> Calling intel_runtime_pm_put() is illegal from a soft-irq context, so
>>> revert the crude hack
>>>
>>> commit aa0b3b5bb8768c1a6a6788869d9c7015eae7e80c
>>> Author: Paulo Zanoni <paulo.r.zanoni at intel.com>
>>> Date:   Tue Apr 1 14:55:07 2014 -0300
>>>
>>>      drm/i915: don't schedule force_wake_timer at gen6_read
>>>
>>> and apply the single line corrective instead.
>>>
>>> References: https://bugs.freedesktop.org/show_bug.cgi?id=80913
>>> Cc: Paulo Zanoni <paulo.r.zanoni at intel.com>
>>> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
>>> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
>>> ---
>>> @@ -777,12 +772,11 @@ gen6_read##x(struct drm_i915_private *dev_priv, off_t reg, bool trace) { \
>>>   	    NEEDS_FORCE_WAKE((dev_priv), (reg))) { \
>>>   		dev_priv->uncore.funcs.force_wake_get(dev_priv, \
>>>   						      FORCEWAKE_ALL); \
>>> -		val = __raw_i915_read##x(dev_priv, reg); \
>>> -		dev_priv->uncore.funcs.force_wake_put(dev_priv, \
>>> -						      FORCEWAKE_ALL); \
>>> -	} else { \
>>> -		val = __raw_i915_read##x(dev_priv, reg); \
>>> +		dev_priv->uncore.forcewake_count++; \
>>> +		mod_timer_pinned(&dev_priv->uncore. , \
>>> +				 jiffies + 1); \
>> why timer, we can do a put after register read right?
> The presumption is that we will do another mmio access requiring the
> forcewake very shortly, and we want to avoid the forcewake clear/ack
> cycle. So we defer dropping the forcewake until the end of the kernel
> context on this cpu (the goal being that as the scheduler switches back
> to the userspace context, we release the wakelock, it would be great if
> there was an explicit callback for that...).
> -Chris

Thanks Chris. got it :)