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

[Joonas Lahtinen <joonas.lahtinen@linux.intel.com>]

On ti, 2015-12-15 at 13:35 +0200, Mika Kuoppala wrote:
> Some igt tests wants to drop caches by writing to this debugfs
> entry. The call to shrinker may ensure and it wants to update
> the fence registers, so hardware access happens. This access
> can happen in a spot where the block containing these registers
> might bepowered down.
> 
> To avoid getting unclaimed register access trace noise due
> to this, take a runtime pm reference during i915_drop_caches set.
> 
> v2: pm_ref and mutex lock ordering (Chris)
> 
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

> Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
> ---
>  drivers/gpu/drm/i915/i915_debugfs.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c
> b/drivers/gpu/drm/i915/i915_debugfs.c
> index 24318b7..d96709a 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -4833,11 +4833,13 @@ i915_drop_caches_set(void *data, u64 val)
>  
>  	DRM_DEBUG("Dropping caches: 0x%08llx\n", val);
>  
> +	intel_runtime_pm_get(dev_priv);
> +
>  	/* No need to check and wait for gpu resets, only libdrm
> auto-restarts
>  	 * on ioctls on -EAGAIN. */
>  	ret = mutex_lock_interruptible(&dev->struct_mutex);
>  	if (ret)
> -		return ret;
> +		goto pm_put;
>  
>  	if (val & DROP_ACTIVE) {
>  		ret = i915_gpu_idle(dev);
> @@ -4856,7 +4858,9 @@ i915_drop_caches_set(void *data, u64 val)
>  
>  unlock:
>  	mutex_unlock(&dev->struct_mutex);
> -
> +pm_put:
> +	intel_runtime_pm_put(dev_priv);
> +	
>  	return ret;
>  }
>  
-- 
Joonas Lahtinen
Open Source Technology Center
Intel Corporation

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