Re: [PATCH RFC 00/12] Add support for DisplayPort link training information report

Dmitry Baryshkov
2026-04-09T21:36:18Z

On Thu, Apr 09, 2026 at 11:36:21PM +0300, Ville Syrjälä wrote:
> On Thu, Apr 09, 2026 at 07:08:16PM +0200, Kory Maincent wrote:
> > DisplayPort link training negotiates the physical-layer parameters needed
> > for a reliable connection: lane count, link rate, voltage swing,
> > pre-emphasis, and optionally Display Stream Compression (DSC). Currently,
> > each driver exposes this state in its own way, often through
> > driver-specific debugfs entries, with no standard interface for userspace
> > diagnostic and monitoring tools.
> >
> > This series introduces a generic, DRM-managed framework for exposing DP
> > link training state as standard connector properties, modeled after the
> > existing HDMI helper drmm_connector_hdmi_init().
> >
> > The new drmm_connector_dp_init() helper initializes a DP connector and
> > registers the following connector properties to expose the negotiated link
> > state to userspace:
> >
> > - num_lanes: negotiated lane count (1, 2 or 4)
> > - link_rate: negotiated link rate
> > - dsc_en: whether Display Stream Compression is active
> > - voltage_swingN: per-lane voltage swing level (lanes 0-3)
> > - pre_emphasisN: per-lane pre-emphasis level (lanes 0-3)
>
> I don't see why any real userspace would be interested in those (apart
> from maybe DSC). If this is just for diagnostics and whatnot then I
> think sysfs/debugfs could be a better fit.

I'd agree here. Please consider implementing it as a debugfs interface,
possibly reusing the Intel's format.

--
With best wishes
Dmitry