Re: [PATCH 1/6] drm/i915: Force the switch to the i915->kernel_context

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

On Thu, 2017-11-02 at 12:42 +0000, Chris Wilson wrote:
> 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.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

<SNIP>

> @@ -1587,8 +1587,20 @@ bool intel_engines_are_idle(struct drm_i915_private *dev_priv)
>  
>  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 *kctx = engine->i915->kernel_context;

*kernel_context = ...

> +	struct drm_i915_gem_request *rq;
> +
> +	lockdep_assert_held(&engine->i915->drm.struct_mutex);
> +
> +	/* An unretired request? */
> +	rq = __i915_gem_active_peek(&engine->timeline->last_request);
> +	if (rq)
> +		return rq->ctx == kctx;
> +
> +	if (!engine->last_retired_context)
> +		return true;
> +
> +	return engine->last_retired_context == kctx;

It might be worthy dropping a comment that a nonexistent context is
considered kernel context to the *cough*nonexistent*cough* kerneldoc.

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

Regards, Joonas
-- 
Joonas Lahtinen
Open Source Technology Center
Intel Corporation
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