Re: [PATCH 4/4] drm/i915: Provide an assert for when we expect forcewake to be held

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

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

> Add assert_forcewakes_active() (the complementary function to
> assert_forcewakes_inactive) that documents the requirement of a
> function for its callers to be holding the forcewake ref (i.e. the
> function is part of a sequence over which RC6 must be prevented).
>
> One such example is during ringbuffer reset, where RC6 must be held
> across the whole reinitialisation sequence.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_ringbuffer.c | 11 ++++++++++-
>  drivers/gpu/drm/i915/intel_uncore.c     | 12 ++++++++++++
>  drivers/gpu/drm/i915/intel_uncore.h     |  2 ++
>  3 files changed, 24 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> index 05c08b0bc172..4285f09ff8b8 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> @@ -579,7 +579,16 @@ static int init_ring_common(struct intel_engine_cs *engine)
>  static void reset_ring_common(struct intel_engine_cs *engine,
>  			      struct drm_i915_gem_request *request)
>  {
> -	/* Try to restore the logical GPU state to match the continuation
> +	/*
> +	 * RC6 must be prevented until the reset is complete and the engine
> +	 * reinitialised. If it occurs in the middle of this sequence, the
> +	 * state written to/loaded from the power context is ill-defined (e.g.
> +	 * the PP_BASE_DIR may be lost).
> +	 */
> +	assert_forcewakes_active(engine->i915, FORCEWAKE_ALL);
> +
> +	/*
> +	 * Try to restore the logical GPU state to match the continuation
>  	 * of the request queue. If we skip the context/PD restore, then
>  	 * the next request may try to execute assuming that its context
>  	 * is valid and loaded on the GPU and so may try to access invalid
> diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> index b3c3f94fc7e4..3d41667919dc 100644
> --- a/drivers/gpu/drm/i915/intel_uncore.c
> +++ b/drivers/gpu/drm/i915/intel_uncore.c
> @@ -629,6 +629,18 @@ void assert_forcewakes_inactive(struct drm_i915_private *dev_priv)
>  	WARN_ON(dev_priv->uncore.fw_domains_active);
>  }
>  
> +void assert_forcewakes_active(struct drm_i915_private *dev_priv,
> +			      enum forcewake_domains fw_domains)
> +{
> +	if (!dev_priv->uncore.funcs.force_wake_get)
> +		return;
> +
> +	assert_rpm_wakelock_held(dev_priv);
> +
> +	fw_domains &= dev_priv->uncore.fw_domains;
> +	WARN_ON(fw_domains & ~dev_priv->uncore.fw_domains_active);
> +}
> +

Adding a debug telling about current domains seems not
to add any value...atleast yet.

I remember yearning after this in the past. 

Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>


>  /* We give fast paths for the really cool registers */
>  #define NEEDS_FORCE_WAKE(reg) ((reg) < 0x40000)
>  
> diff --git a/drivers/gpu/drm/i915/intel_uncore.h b/drivers/gpu/drm/i915/intel_uncore.h
> index 66eae2ce2f29..582771251b57 100644
> --- a/drivers/gpu/drm/i915/intel_uncore.h
> +++ b/drivers/gpu/drm/i915/intel_uncore.h
> @@ -137,6 +137,8 @@ void intel_uncore_resume_early(struct drm_i915_private *dev_priv);
>  
>  u64 intel_uncore_edram_size(struct drm_i915_private *dev_priv);
>  void assert_forcewakes_inactive(struct drm_i915_private *dev_priv);
> +void assert_forcewakes_active(struct drm_i915_private *dev_priv,
> +			      enum forcewake_domains fw_domains);
>  const char *intel_uncore_forcewake_domain_to_str(const enum forcewake_domain_id id);
>  
>  enum forcewake_domains
> -- 
> 2.14.2
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