Re: [PATCH 6/7] drm/i915/fbc: move from crtc_state->enable_fbc to plane_state->enable_fbc

From: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
To: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH 6/7] drm/i915/fbc: move from crtc_state->enable_fbc to plane_state->enable_fbc
Date: Fri, 11 Nov 2016 20:51:29 +0200	[thread overview]
Message-ID: <20161111185129.GS31595@intel.com> (raw)
In-Reply-To: <1478883461-20201-7-git-send-email-paulo.r.zanoni@intel.com>

On Fri, Nov 11, 2016 at 02:57:40PM -0200, Paulo Zanoni wrote:
> Ville pointed out that intel_fbc_choose_crtc() is iterating over all
> planes instead of just the primary planes. There are no real
> consequences of this problem for HSW+, and for the other platforms it
> just means that in some obscure multi-screen cases we'll keep FBC
> disabled when we could have enabled it. Still, iterating over all
> planes doesn't seem to be the best thing to do.
> 
> My initial idea was to just add a check for plane->type and be done,
> but then I realized that in commits not involving the primary plane we
> would reset crtc_state->enable_fbc back to false even when FBC is
> enabled. That also wouldn't result in a bug due to the way the
> enable_fbc variable is checked, but, still, our code can be better
> than this.
> 
> So I went for the solution that involves tracking enable_fbc in the
> primary plane state instead of the CRTC state. This way, if a commit
> doesn't involve the primary plane for the CRTC we won't be resetting
> enable_fbc back to false, so the variable will always reflect the
> reality. And this change also makes more sense since FBC is actually
> tied to the single plane and not the full pipe. As a bonus, we only
> iterate over the CRTCs instead of iterating over all planes.
> 
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Reported-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_drv.h |  4 ++--
>  drivers/gpu/drm/i915/intel_fbc.c | 36 +++++++++++++++++++-----------------
>  2 files changed, 21 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> index 003afb8..025cb74 100644
> --- a/drivers/gpu/drm/i915/intel_drv.h
> +++ b/drivers/gpu/drm/i915/intel_drv.h
> @@ -403,6 +403,8 @@ struct intel_plane_state {
>  	int scaler_id;
>  
>  	struct drm_intel_sprite_colorkey ckey;
> +
> +	bool enable_fbc;
>  };
>  
>  struct intel_initial_plane_config {
> @@ -648,8 +650,6 @@ struct intel_crtc_state {
>  
>  	bool ips_enabled;
>  
> -	bool enable_fbc;
> -
>  	bool double_wide;
>  
>  	bool dp_encoder_is_mst;
> diff --git a/drivers/gpu/drm/i915/intel_fbc.c b/drivers/gpu/drm/i915/intel_fbc.c
> index b095175..fc4ac57 100644
> --- a/drivers/gpu/drm/i915/intel_fbc.c
> +++ b/drivers/gpu/drm/i915/intel_fbc.c
> @@ -1055,16 +1055,17 @@ void intel_fbc_choose_crtc(struct drm_i915_private *dev_priv,
>  			   struct drm_atomic_state *state)
>  {
>  	struct intel_fbc *fbc = &dev_priv->fbc;
> -	struct drm_plane *plane;
> -	struct drm_plane_state *plane_state;
> +	struct drm_crtc *crtc;
> +	struct drm_crtc_state *crtc_state;
>  	bool crtc_chosen = false;
>  	int i;
>  
>  	mutex_lock(&fbc->lock);
>  
> -	/* Does this atomic commit involve the CRTC currently tied to FBC? */
> +	/* Does this atomic commit involve the plane currently tied to FBC? */
>  	if (fbc->crtc &&
> -	    !drm_atomic_get_existing_crtc_state(state, &fbc->crtc->base))
> +	    !drm_atomic_get_existing_plane_state(state,
> +						 fbc->crtc->base.primary))
>  		goto out;
>  
>  	if (!intel_fbc_can_enable(dev_priv))
> @@ -1074,25 +1075,26 @@ void intel_fbc_choose_crtc(struct drm_i915_private *dev_priv,
>  	 * plane. We could go for fancier schemes such as checking the plane
>  	 * size, but this would just affect the few platforms that don't tie FBC
>  	 * to pipe or plane A. */
> -	for_each_plane_in_state(state, plane, plane_state, i) {
> -		struct intel_plane_state *intel_plane_state =
> -			to_intel_plane_state(plane_state);
> -		struct intel_crtc_state *intel_crtc_state;
> -		struct intel_crtc *crtc = to_intel_crtc(plane_state->crtc);
> +	for_each_crtc_in_state(state, crtc, crtc_state, i) {
> +		struct intel_plane_state *plane_state = to_intel_plane_state(
> +			drm_atomic_get_existing_plane_state(state,
> +							    crtc->primary));
> +		struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
>  
> -		if (!intel_plane_state->base.visible)
> +		if (!plane_state)
>  			continue;
>  
> -		if (fbc_on_pipe_a_only(dev_priv) && crtc->pipe != PIPE_A)
> +		if (!plane_state->base.visible)
>  			continue;
>  
> -		if (fbc_on_plane_a_only(dev_priv) && crtc->plane != PLANE_A)
> +		if (fbc_on_pipe_a_only(dev_priv) && intel_crtc->pipe != PIPE_A)
>  			continue;
>  
> -		intel_crtc_state = to_intel_crtc_state(
> -			drm_atomic_get_existing_crtc_state(state, &crtc->base));
> +		if (fbc_on_plane_a_only(dev_priv) &&
> +		    intel_crtc->plane != PLANE_A)
> +			continue;
>  
> -		intel_crtc_state->enable_fbc = true;
> +		plane_state->enable_fbc = true;

So looking at this whole thing, I can't see anything that would prevent
enable_fbc being true for multiple primary planes at the same time
Well, apart from the whole "we enable it only for platforms that can only do
pipe A" thing.

So what happens in that case? FBC just ends up getting enabling on
one of the pipes based on the order intel_fbc_enable() gets called,
or something?

>  		crtc_chosen = true;
>  		break;
>  	}
> @@ -1130,13 +1132,13 @@ void intel_fbc_enable(struct intel_crtc *crtc,
>  	if (fbc->enabled) {
>  		WARN_ON(fbc->crtc == NULL);
>  		if (fbc->crtc == crtc) {
> -			WARN_ON(!crtc_state->enable_fbc);
> +			WARN_ON(!plane_state->enable_fbc);
>  			WARN_ON(fbc->active);
>  		}
>  		goto out;
>  	}
>  
> -	if (!crtc_state->enable_fbc)
> +	if (!plane_state->enable_fbc)
>  		goto out;
>  
>  	WARN_ON(fbc->active);
> -- 
> 2.7.4

-- 
Ville Syrjälä
Intel OTC
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