Re: [Intel-gfx] [PATCH v3 10/11] drm/i915/display: Check if pipe fastset is allowed by external dependencies

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

On Wed, Dec 18, 2019 at 07:00:19PM +0200, Ville Syrjälä wrote:
> On Mon, Dec 16, 2019 at 02:07:41PM -0800, José Roberto de Souza wrote:
> > Check if fastset is allowed by external dependencies like other pipes
> > and transcoders.
> > 
> > Right now this patch only forces a fullmodeset in MST slaves of MST
> > masters that needs a fullmodeset but it will be needed for port sync
> > as well.
> > 
> > v3:
> > - moved handling to intel_atomic_check() this way is guarantee that
> > all pipes will have its state computed
> > 
> > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > Cc: Lucas De Marchi <lucas.demarchi@intel.com>
> > Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> > Cc: Manasi Navare <manasi.d.navare@intel.com>
> > Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_display.c | 63 ++++++++++++++++----
> >  1 file changed, 50 insertions(+), 13 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> > index f1c0687bf69b..2627a7bcb45c 100644
> > --- a/drivers/gpu/drm/i915/display/intel_display.c
> > +++ b/drivers/gpu/drm/i915/display/intel_display.c
> > @@ -13941,19 +13941,6 @@ static void intel_crtc_check_fastset(const struct intel_crtc_state *old_crtc_sta
> >  
> >  	new_crtc_state->uapi.mode_changed = false;
> >  	new_crtc_state->update_pipe = true;
> > -
> > -	/*
> > -	 * If we're not doing the full modeset we want to
> > -	 * keep the current M/N values as they may be
> > -	 * sufficiently different to the computed values
> > -	 * to cause problems.
> > -	 *
> > -	 * FIXME: should really copy more fuzzy state here
> > -	 */
> > -	new_crtc_state->fdi_m_n = old_crtc_state->fdi_m_n;
> > -	new_crtc_state->dp_m_n = old_crtc_state->dp_m_n;
> > -	new_crtc_state->dp_m2_n2 = old_crtc_state->dp_m2_n2;
> > -	new_crtc_state->has_drrs = old_crtc_state->has_drrs;
> >  }
> >  
> >  static int intel_crtc_add_planes_to_state(struct intel_atomic_state *state,
> > @@ -14121,6 +14108,56 @@ static int intel_atomic_check(struct drm_device *dev,
> >  			any_ms = true;
> >  	}
> >  
> > +	/**
> > +	 * Check if fastset is allowed by external dependencies like other
> > +	 * pipes and transcoders.
> > +	 *
> > +	 * Right now it only forces a fullmodeset when the MST master
> > +	 * transcoder did not changed but the pipe of the master transcoder
> > +	 * needs a fullmodeset so all slaves also needs to do a fullmodeset.
> > +	 */
> > +	for_each_new_intel_crtc_in_state(state, crtc, new_crtc_state, i) {
> > +		struct intel_crtc_state *new_crtc_state_iter;
> > +		struct intel_crtc *crtc_iter;
> > +		int j;
> > +
> > +		if (!intel_dp_mst_is_slave_trans(new_crtc_state) ||
> > +		    needs_modeset(new_crtc_state))
> 
> shouldn't this be
> if (!mst_master || !needs_modeset)
> 	continue;
> ?
> 
> > +			continue;
> > +
> > +		for_each_new_intel_crtc_in_state(state, crtc_iter,
> > +						 new_crtc_state_iter, j) {
> > +			if (new_crtc_state->mst_master_transcoder !=
> > +			    new_crtc_state_iter->cpu_transcoder)
> > +				continue;
> > +
> > +			if (needs_modeset(new_crtc_state_iter)) {
> > +				new_crtc_state->uapi.mode_changed = true;
> > +				new_crtc_state->update_pipe = false;
> > +			}
> > +			break;
> 
> Hmm. So I guess the break here is because we're going to keep iterating
> the outer loop anyway? Don't think that works with the s/slave/master/
> fix above.
> 
> I suggest moving this inner loop into a separate function entirely.
> Could simply pass in the master_transcoder to that function and then
> we wouldn't even have this clash with variable names for the two
> crtcs/crtc_states.
> 
> Somethig like (with better funciton names ofc :)
> 
> mst_modeset_slaves(state, master_transcoder)
> {
> 	for_each() {
> 		if (master_transcoder == crtc_state->master_transcoder)
> 			modeset=1;
> 	}
> }
> 
> atomic_check()
> {
> 	for_each()
> 		compute();
> 
> 	for_each() {
> 		if (master && needs_modeset()
> 			mst_modeset_slaves(state, crtc_state->cpu_transcoder);
> 	}
> 
> 	for_each() {
> 		if (fastset)
> 			copy();
> 	}
> }
> 
> Or do we also need to force a modeset for the master if a slave needs a
> modeset? I'm trying to think if there's a way that we could end up with
> a slave changing its master (thus needing modeset) without the master
> being flagged for modeset...

How about this:

1. Enable pipe B (master) + pipe C (slave)
2. Enable pipe A (should become master)

Hmm. Scratch that. Pipe B will have it's master_transcoder change from
INVALID to A so it'll get flagged for a modeset. Seems I need a more
heavy duty thinking cap for this one...

-- 
Ville Syrjälä
Intel
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