Re: [PATCH RFC 09/12] drm: Introduce drmm_connector_dp_init() with link training state properties

Dmitry Baryshkov
2026-04-13T13:59:50Z

On Mon, Apr 13, 2026 at 02:59:30PM +0200, Kory Maincent wrote:
> On Fri, 10 Apr 2026 00:53:08 +0300
> Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com> wrote:
>
> > On Thu, Apr 09, 2026 at 07:08:25PM +0200, Kory Maincent wrote:
> > > Add a managed DisplayPort connector initialization helper,
> > > drmm_connector_dp_init(), modeled after the existing HDMI counterpart
> > > drmm_connector_hdmi_init(). Cleanup is handled automatically via a
> > > DRM-managed action.
> > >
> > > The helper creates the following immutable connector properties to expose
> > > DP link training capabilities and state to userspace:
> > >
> > > - num_lanes: bitmask of supported lane counts (1, 2, 4)
> > > - link_rate: Array of supported link rates.
> > > - dsc_en: Display Stream Compression supported
> > > - voltage_swingN: per-lane voltage swing level bitmask
> > > - pre-emphasisN: per-lane pre-emphasis level bitmask
> > >
> > > Link rates are passed by the driver in deca-kbps, following the DRM
> > > convention, but exposed to userspace in kbps for clarity.
> > >
> > > Two additional helpers are provided to update and reset those properties
> > > at runtime:
> > > - drm_connector_dp_set_link_train_properties()
> > > - drm_connector_dp_reset_link_train_properties()
> > >
>
> ...
>
> > > +/**
> > > + * struct drm_connector_dp_link_train - DRM DisplayPort link training
> > > + * information report
> > > + */
> > > +struct drm_connector_dp_link_train {
> >
> > THese define the current DP state. As such, they definitely make sense
> > to be a part of the drm_connector.
> > > + /**
> > > + * @nlanes: The number of lanes used
> > > + */
> > > + u8 nlanes;
> > > +
> > > + /**
> > > + * @rates: Link rate value selected in deca-kbps
> > > + */
> > > + u32 rate;
> > > +
> > > + /**
> > > + * @dsc: Display Stream Compression enabled
> > > + */
> > > + bool dsc_en;
> > > +
> > > + /**
> > > + * @v_swings: Array listing the bitmask voltage swing level per
> > > lanes
> > > + */
> > > + u8 v_swing[4];
> > > +
> > > + /**
> > > + * @pre_emph: Array listing the bitmask pre-emphasis level per
> > > lanes
> > > + */
> > > + u8 pre_emph[4];
> >
> > Please consider following struct phy_configure_opts_dp (or using it as
> > is). Overall, please refer the talk and (more important) the lightning
> > resumee at this XDC. I have some bits and pieces ready in spite of that
> > proposal, but I didn't have time to finish it.
>
> I didn't know this phy_configure_opts_dp struct. This indeed could make sense
> to reuse and modify that structure for our needs.

Why would you want to modify it? It is an interface for the PHY drivers.
Is there anything that you miss there?

> About your XDC talk. What were the developments you were talking about? Could I
> have a look at them?

I've posted an RFC just before the XDC. Currently I'm looking at the
link training generification. Overall, you don't have to wait for that
job to be completed, just take some of the notes in account (like reuse
of the PHY config structures).

>
> Regards,
> --
> Köry Maincent, Bootlin
> Embedded Linux and kernel engineering
> https://bootlin.com

--
With best wishes
Dmitry