[Intel-gfx] [PATCH v2 2/9] drm/i915: Force the switch to the i915->kernel_context

[Mika Kuoppala]

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

> In the next few patches, we will have a hard requirement that we emit a
> context-switch to the perma-pinned i915->kernel_context (so that we can
> save the HW state using that context-switch). As the first context
> itself may be classed as a kernel context, we want to be explicit in our
> comparison. For an extra-layer of finesse, we can check the last
> unretired context on the engine; as well as the last retired context
> when idle.
>
> v2: verbose verbosity
> v3: Always force the switch, even when the engine is idle, and update
> the assert that this happens before suspend.
>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> Reviewed-by: Joonas Lahtinen <joonas.lahtinen at linux.intel.com> #v1
> ---
>  drivers/gpu/drm/i915/i915_gem.c        | 10 ++++++----
>  drivers/gpu/drm/i915/intel_engine_cs.c | 26 ++++++++++++++++++++++++--
>  2 files changed, 30 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 9470ba0c1930..fe312ab3b664 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -4687,14 +4687,16 @@ void __i915_gem_object_release_unless_active(struct drm_i915_gem_object *obj)
>  		i915_gem_object_put(obj);
>  }
>  
> -static void assert_kernel_context_is_current(struct drm_i915_private *dev_priv)
> +static void assert_kernel_context_is_current(struct drm_i915_private *i915)
>  {
> +	struct i915_gem_context *kernel_context = i915->kernel_context;
>  	struct intel_engine_cs *engine;
>  	enum intel_engine_id id;
>  
> -	for_each_engine(engine, dev_priv, id)
> -		GEM_BUG_ON(engine->last_retired_context &&
> -			   !i915_gem_context_is_kernel(engine->last_retired_context));
> +	for_each_engine(engine, i915, id) {
> +		GEM_BUG_ON(__i915_gem_active_peek(&engine->timeline->last_request));

It could be that we have a active request for kernel context and we
still bail out with assert. Why?

-Mika

> +		GEM_BUG_ON(engine->last_retired_context != kernel_context);
> +	}
>  }
>  
>  void i915_gem_sanitize(struct drm_i915_private *i915)
> diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
> index 0987768c311d..374e398e867a 100644
> --- a/drivers/gpu/drm/i915/intel_engine_cs.c
> +++ b/drivers/gpu/drm/i915/intel_engine_cs.c
> @@ -1593,10 +1593,32 @@ bool intel_engines_are_idle(struct drm_i915_private *dev_priv)
>  	return true;
>  }
>  
> +/**
> + * intel_engine_has_kernel_context:
> + * @engine: the engine
> + *
> + * Returns true if the last context to be executed on this engine, or has been
> + * executed if the engine is already idle, is the kernel context
> + * (#i915.kernel_context).
> + */
>  bool intel_engine_has_kernel_context(const struct intel_engine_cs *engine)
>  {
> -	return (!engine->last_retired_context ||
> -		i915_gem_context_is_kernel(engine->last_retired_context));
> +	const struct i915_gem_context * const kernel_context =
> +		engine->i915->kernel_context;
> +	struct drm_i915_gem_request *rq;
> +
> +	lockdep_assert_held(&engine->i915->drm.struct_mutex);
> +
> +	/*
> +	 * Check the last context seen by the engine. If active, it will be
> +	 * the last request that remains in the timeline. When idle, it is
> +	 * the last executed context as tracked by retirement.
> +	 */
> +	rq = __i915_gem_active_peek(&engine->timeline->last_request);
> +	if (rq)
> +		return rq->ctx == kernel_context;
> +	else
> +		return engine->last_retired_context == kernel_context;
>  }
>  
>  void intel_engines_reset_default_submission(struct drm_i915_private *i915)
> -- 
> 2.15.0
>
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