Re: [PATCH 1/6] drm/i915: Get runtime pm ref on i915_drop_caches_set

[Mika Kuoppala <mika.kuoppala@linux.intel.com>]

Chris Wilson <chris@chris-wilson.co.uk> writes:

> On Mon, Dec 14, 2015 at 07:14:23PM +0200, Mika Kuoppala wrote:
>> When we drop caches, this debugfs entry does hardware access later in
>> the chain, when fences are updated, so it needs a runtime pm ref.
>> 
>> Dropping caches is used by some igt/bat tests, so this fixes
>> some unclaimed register access traces.
>> 
>> Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
>> ---
>>  drivers/gpu/drm/i915/i915_debugfs.c | 3 +++
>>  1 file changed, 3 insertions(+)
>> 
>> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
>> index 24318b7..bd8ba7e 100644
>> --- a/drivers/gpu/drm/i915/i915_debugfs.c
>> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
>> @@ -4839,6 +4839,8 @@ i915_drop_caches_set(void *data, u64 val)
>>  	if (ret)
>>  		return ret;
>>  
>> +	intel_runtime_pm_get(dev_priv);
>
> The current idea of the very coarse granularity of rpm_get() is to do it
> before struct_mutex (since rpm_get resume may try to acquire the mutex
> iirc).
>
> Ok, fixing that may be bolting the stable door after the horse bolted,
> but we should nevertheless. In my opinion, it would be more productive
> to work with Imre on making rpm fine grained so that we don't so many
> and can actually place the wakelock around the hardware access itself,
> not every single path that *may* touch hardware.

Please consider 1/6 v2 as it is needed to avoid random unclaimed
accesses during igt/bat if the drop caches is used in wrong spot.

We can forget the rest.

-Mika



> -Chris
>
> -- 
> Chris Wilson, Intel Open Source Technology Centre
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