[Intel-gfx] [PATCH 8/8] drm/i915: Keep track of reserved execlist ports

[Chris Wilson]

Quoting Mika Kuoppala (2017-09-12 09:36:18)
> +execlist_request_port(struct intel_engine_execlist * const el)
> +{
> +       GEM_DEBUG_BUG_ON(el->port_count == el->port_mask + 1);
> +
> +       el->port_count++;
> +
> +       GEM_DEBUG_BUG_ON(port_isset(execlist_port_tail(el)));
> +
> +       return execlist_port_tail(el);
> +}
> 
> diff --git a/drivers/gpu/drm/i915/i915_guc_submission.c b/drivers/gpu/drm/i915/i915_guc_submission.c
> index 0dfb03a0cee4..fdda3a1835ad 100644
> --- a/drivers/gpu/drm/i915/i915_guc_submission.c
> +++ b/drivers/gpu/drm/i915/i915_guc_submission.c
> @@ -662,12 +662,19 @@ static void port_assign(struct execlist_port *port,
>  static bool i915_guc_dequeue(struct intel_engine_cs *engine)
>  {
>         struct intel_engine_execlist * const el = &engine->execlist;
> -       struct execlist_port *port = execlist_port_head(el);
> -       const struct execlist_port * const last_port = execlist_port_tail(el);
> -       struct drm_i915_gem_request *last = port_request(port);
> +       struct execlist_port *port;
> +       struct drm_i915_gem_request *last;
>         struct rb_node *rb;
>         bool submit = false;
>  
> +       if (execlist_active_ports(el)) {
> +               port = execlist_port_tail(el);
> +               last = port_request(port);
> +       } else {
> +               port = NULL;
> +               last = NULL;
> +       }
> +
>         spin_lock_irq(&engine->timeline->lock);
>         rb = el->first;
>         GEM_BUG_ON(rb_first(&el->queue) != rb);
> @@ -675,9 +682,12 @@ static bool i915_guc_dequeue(struct intel_engine_cs *engine)
>                 struct i915_priolist *p = rb_entry(rb, typeof(*p), node);
>                 struct drm_i915_gem_request *rq, *rn;
>  
> +               if (!port)
> +                       port = execlist_request_port(el);
> +

I can't see port becoming NULL inside the loop, so why can't we do it
during the init above? What did I miss?
-Chris