Re: [PATCH v4 06/18] drm/bridge: aux-hpd: Support USB Type-C DP altmodes via DRM lane assignment

[Andy Shevchenko]

On Tue, Sep 03, 2024 at 06:20:14PM -0400, Stephen Boyd wrote:
> Quoting Andy Shevchenko (2024-09-02 04:35:46)
> > On Sat, Aug 31, 2024 at 09:06:44PM -0700, Stephen Boyd wrote:

> > > Extend the aux-hpd bridge driver to support assigning DP lanes to USB
> > > type-c pins based on typec mux state entry. Existing users of this
> > > driver only need the HPD signaling support, so leave that in place and
> > > wrap the code with a variant that supports more features of USB type-c
> >
> > Isn't the proper spelling "USB Type-C"?
> 
> Perhaps in a title?

I am talking about the commit message :-)

> > > DP altmode, i.e. pin configurations. Prefix that code with
> > > 'drm_dp_typec_bridge' to differentiate it from the existing
> > > 'drm_aux_hpd_bridge' code.
> > >
> > > Parse the struct typec_mux_state members to determine if DP altmode has
> > > been entered and if HPD is asserted or not. Signal HPD to the drm bridge
> > > chain when HPD is asserted. Similarly, parse the pin assignment and map
> > > the DP lanes to the usb-c output lanes, taking into account any lane
> > > remapping from the data-lanes endpoint property. Pass that lane mapping
> > > to the previous drm_bridge in the bridge chain during the atomic check
> > > phase.

...

> > > +     adev->dev.of_node = of_node_get(parent->of_node);
> >
> > device_set_node() ?
> 
> Or device_set_of_node_from_dev()?

This is quite unclear to me. The second one bumps the reference count IIRC
for no reason (in usual cases). Also only few drivers use that, I would hear
what OF people can tell about this API and its usage scope.

...

> > > +static int dp_lane_to_typec_lane(enum dp_lane lane)
> > > +{
> > > +     switch (lane) {
> > > +     case DP_ML0:
> > > +             return USB_SSTX2;
> > > +     case DP_ML1:
> > > +             return USB_SSRX2;
> > > +     case DP_ML2:
> > > +             return USB_SSTX1;
> > > +     case DP_ML3:
> > > +             return USB_SSRX1;
> > > +     }
> >
> > > +     return -EINVAL;
> >
> > Hmm... This can be simply made as default case.
> 
> And then the enum is always "covered" and the compiler doesn't complain
> about missing cases (I don't think we have -Wswitch-enum)? Seems worse.

Hmm... You mean if I remove one of the above cases I will get the warning?

> > > +}

-- 
With Best Regards,
Andy Shevchenko