Re: [PATCH v6 1/8] drm/msm/dp: Add eDP support via aux_bus

[Dmitry Baryshkov]

On Fri, 8 Apr 2022 at 03:26, Doug Anderson <dianders@xxxxxxxxxxxx> wrote:
>
> Hi,
>
> On Thu, Apr 7, 2022 at 4:46 PM Dmitry Baryshkov
> <dmitry.baryshkov@xxxxxxxxxx> wrote:
> >
> > > The way I'm arguing it should work is that:
> > >
> > > 1. A whole bunch of the DP init code should move to the DP driver's
> > > probe function. This includes parsing the DT, acquiring clocks,
> > > getting a handle to our PHY, and IO mapping registers. As far as I
> > > know, there's no reason to wait on all the components being probed in
> > > order to do this stuff.
> >
> > Yes. And that's one of the reasons I tried to stay away from the DP
> > driver. Each time I open the source code, my hands itch to start
> > refactoring the code.
> >
> > >
> > > 2. Once we have done the above things, it should be possible to do AUX
> > > transfers, correct? ...and then we can populate the AUX bus from the
> > > probe function too.
> >
> > No. In the DP case the AUX bus is inaccessible until the dongle is
> > plugged (see all the HPD handling, phy_init()/phy_power_on() is hidden
> > somewhere in that path)
>
> I guess my thought was that in DP you could still create the AUX bus
> at probe time. Then for DP you just return an instant "transfer
> failed" from the AUX bus if HPD isn't asserted. For eDP (as discussed
> elsewhere) when we try to do an AUX transfer then we delay until HPD
> is there.

I think panel-edp would already handle the delay, so we do not need to
have this logic in the DP driver.

> So we can still acquire resources (clocks, PHY, io maps, etc) at probe
> time for DP and create the AUX bus, right? It will just return
> "-ENODEV" if HPD isn't asserted and you're DP?

Yes, please. I still suppose that we'd need a separate case to
power_on eDP's PHY during the probe time. Maybe I'm mistaken here.

-- 
With best wishes
Dmitry