Re: [PATCH] drm/i915: Fix up the inverse mapping for default ctx->engines[]

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

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

> The order in which we store the engines inside default_engines() for the
> legacy ctx->engines[] has to match the legacy I915_EXEC_RING selector
> mapping in execbuf::user_map. If we present VCS2 as being the second
> instance of the video engine, legacy userspace calls that I915_EXEC_BSD2
> and so we need to insert it into the second video slot.
>
> Fixes: 2edda80db3d0 ("drm/i915: Rename engines to match their user interface")
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
> ---
> Contract the static mapping table.
> ---
>  drivers/gpu/drm/i915/gem/i915_gem_context.c |  5 ++-
>  drivers/gpu/drm/i915/gt/intel_engine_user.c | 49 +++++++++++++++++++++
>  drivers/gpu/drm/i915/gt/intel_gt_types.h    |  1 +
>  3 files changed, 53 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> index 1c5bc21a80ff..fae8ca72e240 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> @@ -279,6 +279,7 @@ static void free_engines_rcu(struct rcu_head *rcu)
>  
>  static struct i915_gem_engines *default_engines(struct i915_gem_context *ctx)
>  {
> +	const struct intel_gt *gt = &ctx->i915->gt;
>  	struct intel_engine_cs *engine;
>  	struct i915_gem_engines *e;
>  	enum intel_engine_id id;
> @@ -288,7 +289,7 @@ static struct i915_gem_engines *default_engines(struct i915_gem_context *ctx)
>  		return ERR_PTR(-ENOMEM);
>  
>  	init_rcu_head(&e->rcu);
> -	for_each_engine(engine, ctx->i915, id) {
> +	for_each_engine(engine, gt, id) {

Don't know yet if I love it or hate it.

As I got bruised I started yearning for intel_legacy_engine_id
with a strong type.

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

>  		struct intel_context *ce;
>  
>  		ce = intel_context_create(ctx, engine);
> @@ -298,8 +299,8 @@ static struct i915_gem_engines *default_engines(struct i915_gem_context *ctx)
>  		}
>  
>  		e->engines[id] = ce;
> +		e->num_engines = id + 1;
>  	}
> -	e->num_engines = id;
>  
>  	return e;
>  }
> diff --git a/drivers/gpu/drm/i915/gt/intel_engine_user.c b/drivers/gpu/drm/i915/gt/intel_engine_user.c
> index c41ae05988a5..83dbc54c3d2a 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine_user.c
> +++ b/drivers/gpu/drm/i915/gt/intel_engine_user.c
> @@ -142,8 +142,54 @@ const char *intel_engine_class_repr(u8 class)
>  	return uabi_names[class];
>  }
>  
> +struct legacy_ring {
> +	struct intel_gt *gt;
> +	u8 class;
> +	u8 instance;
> +};
> +
> +static int legacy_ring_id(const struct legacy_ring *ring)
> +{
> +	static const struct {
> +		u8 base, max;
> +	} map[] = {
> +		[RENDER_CLASS] = { RCS0, 1 },
> +		[COPY_ENGINE_CLASS] = { BCS0, 1 },
> +		[VIDEO_DECODE_CLASS] = { VCS0, I915_MAX_VCS },
> +		[VIDEO_ENHANCEMENT_CLASS] = { VECS0, I915_MAX_VECS },
> +	};
> +
> +	if (GEM_DEBUG_WARN_ON(ring->class >= ARRAY_SIZE(map)))
> +		return -1;
> +
> +	if (GEM_DEBUG_WARN_ON(ring->instance >= map[ring->class].max))
> +		return -1;
> +
> +	return map[ring->class].base + ring->instance;
> +}
> +
> +static void add_legacy_ring(struct legacy_ring *ring,
> +			    struct intel_engine_cs *engine)
> +{
> +	int id;
> +
> +	if (engine->gt != ring->gt || engine->class != ring->class) {
> +		ring->gt = engine->gt;
> +		ring->class = engine->class;
> +		ring->instance = 0;
> +	}
> +
> +	id = legacy_ring_id(ring);
> +	if (unlikely(id == -1))
> +		return;
> +
> +	ring->gt->engine[id] = engine;
> +	ring->instance++;
> +}
> +
>  void intel_engines_driver_register(struct drm_i915_private *i915)
>  {
> +	struct legacy_ring ring = {};
>  	u8 uabi_instances[4] = {};
>  	struct list_head *it, *next;
>  	struct rb_node **p, *prev;
> @@ -179,6 +225,9 @@ void intel_engines_driver_register(struct drm_i915_private *i915)
>  						    engine->uabi_class,
>  						    engine->uabi_instance) != engine);
>  
> +		/* Fix up the mapping to match default execbuf::user_map[] */
> +		add_legacy_ring(&ring, engine);
> +
>  		prev = &engine->uabi_node;
>  		p = &prev->rb_right;
>  	}
> diff --git a/drivers/gpu/drm/i915/gt/intel_gt_types.h b/drivers/gpu/drm/i915/gt/intel_gt_types.h
> index 5fd11e361d03..789102f4f46b 100644
> --- a/drivers/gpu/drm/i915/gt/intel_gt_types.h
> +++ b/drivers/gpu/drm/i915/gt/intel_gt_types.h
> @@ -78,6 +78,7 @@ struct intel_gt {
>  
>  	u32 pm_guc_events;
>  
> +	struct intel_engine_cs *engine[I915_NUM_ENGINES];
>  	struct intel_engine_cs *engine_class[MAX_ENGINE_CLASS + 1]
>  					    [MAX_ENGINE_INSTANCE + 1];
>  };
> -- 
> 2.23.0.rc1
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