Re: [PATCH] drm/msm/dp: remove limitation of link rate at 5.4G to support HBR3

[Kuogee Hsieh]

On 11/2/2022 11:04 AM, Dmitry Baryshkov wrote:
> On 02/11/2022 20:28, Doug Anderson wrote:
> > Hi,
> >
> > On Wed, Nov 2, 2022 at 10:23 AM Dmitry Baryshkov
> > <dmitry.baryshkov@xxxxxxxxxx> wrote:
> > > > 1. Someone figures out how to model this with the bridge chain and
> > > > then we only allow HBR3 if we detect we've got a TCPC that supports
> > > > it. This seems like the cleanest / best but feels like a long pole.
> > > > Not only have we been trying to get the TCPC-modeled-as-a-bridge stuff
> > > > landed for a long time but even when we do it we still don't have a
> > > > solution for how to communicate the number of lanes and other stuff
> > > > between the TCPC and the DP controller so we have to enrich the bridge
> > > > interface.
> > >
> > > I think we'd need some OOB interface. For example for DSI interfaces we
> > > have mipi_dsi_device struct to communicate such OOB data.
> > >
> > > Also take a note regarding data-lanes from my previous email.
> >
> > Right, we can somehow communicate the max link rate through the bridge
> > chain to the DP controller in an OOB manner that would work.
>
> I'd note that our dp_panel has some notion of such OOB data. So do AUX 
> drivers including the panel-edp. My suggestion would be to consider 
> both of them while modelling the OOB data.
>
> > > > 2. We add in a DT property to the display controller node that says
> > > > the max link rate for use on this board. This feels like a hack, but
> > > > maybe it's not too bad. Certainly it would be incredibly simple to
> > > > implement. Actually... ...one could argue that even if we later model
> > > > the TCPC as a bridge that this property would still be valid / useful!
> > > > You could certainly imagine that the SoC supports HBR3 and the TCPC
> > > > supports HBR3 but that the board routing between the SoC and the TCPC
> > > > is bad and only supports HBR2. In this case the only way out is
> > > > essentially a "board constraint" AKA a DT property in the DP
> > > > controller.
> > >
> > > We have been discussing similar topics with Abhinav. Krzysztof 
> > > suggested
> > > using link-frequencies property to provide max and min values.

questions,

1)is Krzysztof suggested had been implemented?

2) where is link property i can add link-frequencies?


> > This sounds good to me and seems worth doing even if we eventually do 
> > #1.
>
> And the bonus point is that it can be done easily.