Re: [Intel-gfx] [PATCH v21 05/10] drm/i915: Extract gen specific functions from intel_can_enable_sagv

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Apr 08, 2020 at 10:58:04AM +0300, Lisovskiy, Stanislav wrote:
> On Tue, Apr 07, 2020 at 10:01:28PM +0300, Ville Syrjälä wrote:
> > On Fri, Apr 03, 2020 at 09:20:03AM +0300, Stanislav Lisovskiy wrote:
> > > Addressing one of the comments, recommending to extract platform
> > > specific code from intel_can_enable_sagv as a preparation, before
> > > we are going to add support for tgl+.
> > > 
> > > Current code in intel_can_enable_sagv is valid only for skl,
> > > so this patch adds also proper support for icl, subsequent
> > > patches will add support for tgl+, combined with other required
> > > changes.
> > > 
> > > v2: - Renamed icl_can_enable_sagv into icl_crtc_can_enable_sagv(Ville)
> > >     - Removed dev variables(Ville)
> > >     - Constified crtc/plane_state in icl_crtc_can_enable_sagv
> > >       function(Ville)
> > >     - Added hw.active check(Ville)
> > >     - Refactored if ladder(Ville)
> > > 
> > > Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
> > > ---
> > >  drivers/gpu/drm/i915/intel_pm.c | 84 +++++++++++++++++++++------------
> > >  1 file changed, 55 insertions(+), 29 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> > > index f8d62d1977ac..27d4d626cb34 100644
> > > --- a/drivers/gpu/drm/i915/intel_pm.c
> > > +++ b/drivers/gpu/drm/i915/intel_pm.c
> > > @@ -3757,42 +3757,25 @@ intel_disable_sagv(struct drm_i915_private *dev_priv)
> > >  	return 0;
> > >  }
> > >  
> > > -bool intel_can_enable_sagv(struct intel_atomic_state *state)
> > > +static bool icl_crtc_can_enable_sagv(const struct intel_crtc_state *crtc_state)
> > >  {
> > > -	struct drm_device *dev = state->base.dev;
> > > -	struct drm_i915_private *dev_priv = to_i915(dev);
> > > -	struct intel_crtc *crtc;
> > > +	struct drm_i915_private *dev_priv = to_i915(crtc_state->uapi.crtc->dev);
> > > +	struct intel_crtc *crtc = to_intel_crtc(crtc_state->uapi.crtc);
> > >  	struct intel_plane *plane;
> > > -	struct intel_crtc_state *crtc_state;
> > > -	enum pipe pipe;
> > > +	const struct intel_plane_state *plane_state;
> > >  	int level, latency;
> > >  
> > > -	if (!intel_has_sagv(dev_priv))
> > > +	if (crtc_state->hw.adjusted_mode.flags & DRM_MODE_FLAG_INTERLACE) {
> > > +		DRM_DEBUG_KMS("No SAGV for interlaced mode on pipe %c\n",
> > > +			      pipe_name(crtc->pipe));
> > >  		return false;
> > > +	}
> > >  
> > > -	/*
> > > -	 * If there are no active CRTCs, no additional checks need be performed
> > > -	 */
> > > -	if (hweight8(state->active_pipes) == 0)
> > > +	if (!crtc_state->hw.active)
> > 
> > Should really be checked before anything else. Doesn't matter too much
> > anymore since I made us clear the crtc state always, but still a bit
> > inconsistent to look at other stuff in the state before we even know if
> > the crtc is even enabled.
> > 
> > >  		return true;
> > >  
> > > -	/*
> > > -	 * SKL+ workaround: bspec recommends we disable SAGV when we have
> > > -	 * more then one pipe enabled
> > > -	 */
> > > -	if (hweight8(state->active_pipes) > 1)
> > > -		return false;
> > > -
> > > -	/* Since we're now guaranteed to only have one active CRTC... */
> > > -	pipe = ffs(state->active_pipes) - 1;
> > > -	crtc = intel_get_crtc_for_pipe(dev_priv, pipe);
> > > -	crtc_state = to_intel_crtc_state(crtc->base.state);
> > > -
> > > -	if (crtc_state->hw.adjusted_mode.flags & DRM_MODE_FLAG_INTERLACE)
> > > -		return false;
> > > -
> > > -	for_each_intel_plane_on_crtc(dev, crtc, plane) {
> > > -		struct skl_plane_wm *wm =
> > > +	intel_atomic_crtc_state_for_each_plane_state(plane, plane_state, crtc_state) {
> > > +		const struct skl_plane_wm *wm =
> > >  			&crtc_state->wm.skl.optimal.planes[plane->id];
> > >  
> > >  		/* Skip this plane if it's not enabled */
> > > @@ -3807,7 +3790,7 @@ bool intel_can_enable_sagv(struct intel_atomic_state *state)
> > >  		latency = dev_priv->wm.skl_latency[level];
> > >  
> > >  		if (skl_needs_memory_bw_wa(dev_priv) &&
> > > -		    plane->base.state->fb->modifier ==
> > > +		    plane_state->uapi.fb->modifier ==
> > 
> > hw.fb
> > 
> > With those this is basically good, but still need to think how to avoid
> > the regression due to only checking the crtcs in the state.
> 
> Well tbh, initially you told me that this *_crtc_can_enable_sagv function extraction
> can be "trivially" done as a separate patch :)) So I followed your instruction, and 
> then I got a comment saying that "this is now temporary busted because we are checking
> only crtcs in a state". This kind of contraversial requirements - in order not to 
> have it "temporary busted", we should have introduced it at the same time with SAGV mask,
> at the same time you wanted it to be extracted as a separate patch.

TBF this patch does quite a bit more than extract the current code.

What I think would work as a series is something like:
patch 1:
+intel_crtc_can_enable_sagv(crtc_state)
{
+	stuff
}

intel_can_enable_sagv(state)
{
	...
	crtc_state = to_intel_crtc_state(crtc->base.state);

-	stuff
+	return intel_crtc_can_eanble_sagv(crtc_state);
}

patch 2:
+sagv_pre_plane_update(state)
+{
+	if (!intel_can_enable_sagv(state))
+		intel_disable_sagv(dev_priv);
+}

intel_atomic_commit_tail()
{
	...
-	if (!intel_can_enable_sagv(state))
-		intel_disable_sagv(dev_priv);
+	sagv_pre_plane_update(state);
	...
}

(+ identical changes for post_plane_update())

So far everything has been pure refactoring.

patch 3:
Introduce the sagv mask in bw state and precompute it using
intel_crtc_can_enable_sagv() (while fixing the iterator issue therein),
and update the pre/post hooks to consult said mask. Not quite pure
refactoring anymore but seems like a bit more straightforward change
now.

At this point we should have a nicely precomputed sagv mask without
intentional changes to current behaviour. After which it should be
easier to extend this for new platforms.

-- 
Ville Syrjälä
Intel
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