Re: [Intel-gfx] [PATCH v3 18/25] drm/i915/dp_mst: Add atomic state for all streams on pre-tgl platforms

["Lisovskiy, Stanislav" <stanislav.lisovskiy@intel.com>]

On Wed, Sep 20, 2023 at 03:38:05PM +0300, Imre Deak wrote:
> On Wed, Sep 20, 2023 at 02:25:14PM +0300, Lisovskiy, Stanislav wrote:
> > On Wed, Sep 20, 2023 at 01:59:53PM +0300, Ville Syrjälä wrote:
> > > On Wed, Sep 20, 2023 at 12:11:58PM +0300, Lisovskiy, Stanislav wrote:
> > > > On Thu, Sep 14, 2023 at 10:26:52PM +0300, Imre Deak wrote:
> > > > > If an MST stream is modeset, its state must be checked along all the
> > > > > other streams on the same MST link, for instance to resolve a BW
> > > > > overallocation of a non-sink MST port or to make sure that the FEC is
> > > > > enabled/disabled the same way for all these streams.
> > > > > 
> > > > > To prepare for that this patch adds all the stream CRTCs to the atomic
> > > > > state and marks them for modeset similarly to tgl+ platforms. (If the
> > > > > state computation doesn't change the state the CRTC is switched back to
> > > > > fastset mode.)
> > > > > 
> > > > > Signed-off-by: Imre Deak <imre.deak@intel.com>
> > > > > ---
> > > > >  drivers/gpu/drm/i915/display/intel_dp_mst.c | 3 ---
> > > > >  1 file changed, 3 deletions(-)
> > > > > 
> > > > > diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> > > > > index c1fea894d3774..832e8b0e87e84 100644
> > > > > --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> > > > > +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> > > > > @@ -491,9 +491,6 @@ intel_dp_mst_atomic_master_trans_check(struct intel_connector *connector,
> > > > >  	struct intel_connector *connector_iter;
> > > > >  	int ret = 0;
> > > > >  
> > > > > -	if (DISPLAY_VER(dev_priv) < 12)
> > > > > -		return  0;
> > > > > -
> > > > 
> > > > I'm just a bit concerned, why this check was initially added?
> > > > Probably there was a reason?
> > > 
> > > It's in the name of the function, which should be renamed if we're
> > > extending it beyond its original purpose.
> > 
> > Well, I would say this check could be "a bit" more descriptive.
> > Still, even if function name gets changed, we just remove the check, for the
> > function which was initially not even intended to be called for pre-tgl?
> 
> The change on tgl+ platforms is that all the MST streams go through a
> master transcoder, while on old platforms each stream has only its own
> transcoder. Hence on tgl+ all streams/CRTCs may need to be modeset, at
> least in the case the CRTC owning the master transcoder (for instance
> pipe A/transcoder A) is modeset. So on tgl+ here all CRTCs for a given
> MST topology is added to the state/marked for modeset.
> 
> pre-tgl this wasn't necessary, until the need to recalculate the BW
> requirement of each stream came up, as described in the commit log.
> 
> I can clarify the above in the commit log and rename the function
> accordingly, is that ok?

Yes, thank you for good explanation. I would may be also add some note to
actual function also, but up to you really.

Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>

> 
> > Why it became suitable now then? Or was it just wrong check?
> > 
> > Stan
> > 
> > > 
> > > > 
> > > > Stan
> > > > 
> > > > >  	if (!intel_connector_needs_modeset(state, &connector->base))
> > > > >  		return 0;
> > > > >  
> > > > > -- 
> > > > > 2.37.2
> > > > > 
> > > 
> > > -- 
> > > Ville Syrjälä
> > > Intel