[PATCH 27/27] drm: Add default modes for connectors in unknown state

Wed Jun 24 19:31:46 UTC 2020

On Wed, Jun 24, 2020 at 5:24 PM Alex Deucher <alexdeucher at gmail.com> wrote:
>
> On Wed, Jun 24, 2020 at 3:23 AM Daniel Vetter <daniel at ffwll.ch> wrote:
> >
> > On Wed, Jun 24, 2020 at 04:12:09AM +0300, Laurent Pinchart wrote:
> > > Hi Sam,
> > >
> > > On Sun, Jun 21, 2020 at 10:40:00AM +0200, Sam Ravnborg wrote:
> > > > On Tue, May 26, 2020 at 04:15:05AM +0300, Laurent Pinchart wrote:
> > > > > The DRM CRTC helpers add default modes to connectors in the connected
> > > > > state if no mode can be retrieved from the connector. This behaviour is
> > > > > useful for VGA or DVI outputs that have no connected DDC bus. However,
> > > > > in such cases, the status of the output usually can't be retrieved and
> > > > > is reported as connector_status_unknown.
> > > > >
> > > > > Extend the addition of default modes to connectors in an unknown state
> > > > > to support outputs that can retrieve neither the modes nor the
> > > > > connection status.
> > > > >
> > > > > Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas at ideasonboard.com>
> > > >
> > > > From your description sounds like an OK approach.
> > > > But this is not something I feel too familiar with.
> > > > Acked-by: Sam Ravnborg <sam at ravnborg.org>
> > >
> > > Thanks for the ack. I'd like to have Daniel's (CC'ed) feedback on this
> > > too.
> >
> > Makes sense, and at least pre-coffee me can't immediately think of a
> > scenario where we're going to regret this. _unknown status is pretty much
> > limited to old VGA and similar things where load detect somehow isn't well
> > supported by the hw.
> >
> > Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> >
> > >
> > > > > ---
> > > > >  drivers/gpu/drm/drm_probe_helper.c       | 3 ++-
> > > > >  include/drm/drm_modeset_helper_vtables.h | 8 +++++++-
> > > > >  2 files changed, 9 insertions(+), 2 deletions(-)
> > > > >
> > > > > diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
> > > > > index f5d141e0400f..9055d9573c90 100644
> > > > > --- a/drivers/gpu/drm/drm_probe_helper.c
> > > > > +++ b/drivers/gpu/drm/drm_probe_helper.c
> > > > > @@ -491,7 +491,8 @@ int drm_helper_probe_single_connector_modes(struct drm_connector *connector,
> > > > >   if (count == 0 && connector->status == connector_status_connected)
> > > > >           count = drm_add_override_edid_modes(connector);
> > > > >
> > > > > - if (count == 0 && connector->status == connector_status_connected)
> > > > > + if (count == 0 && (connector->status == connector_status_connected ||
> > > > > +                    connector->status == connector_status_unknown))
> > > > >           count = drm_add_modes_noedid(connector, 1024, 768);
> > > > >   count += drm_helper_probe_add_cmdline_mode(connector);
> > > > >   if (count == 0)
> > > > > diff --git a/include/drm/drm_modeset_helper_vtables.h b/include/drm/drm_modeset_helper_vtables.h
> > > > > index 421a30f08463..afe55e2e93d2 100644
> > > > > --- a/include/drm/drm_modeset_helper_vtables.h
> > > > > +++ b/include/drm/drm_modeset_helper_vtables.h
> > > > > @@ -876,13 +876,19 @@ struct drm_connector_helper_funcs {
> > > > >    * The usual way to implement this is to cache the EDID retrieved in the
> > > > >    * probe callback somewhere in the driver-private connector structure.
> > > > >    * In this function drivers then parse the modes in the EDID and add
> > > > > -  * them by calling drm_add_edid_modes(). But connectors that driver a
> > > > > +  * them by calling drm_add_edid_modes(). But connectors that drive a
> > > > >    * fixed panel can also manually add specific modes using
> > > > >    * drm_mode_probed_add(). Drivers which manually add modes should also
> > > > >    * make sure that the &drm_connector.display_info,
> > > > >    * &drm_connector.width_mm and &drm_connector.height_mm fields are
> > > > >    * filled in.
> > > > >    *
> > > > > +  * Note that the caller function will automatically add standard VESA
> > > > > +  * DMT modes up to 1024x768 if the .get_modes() helper operation returns
> > > > > +  * no mode and if the connector status is connector_status_connected or
> > > > > +  * connector_status_unknown. There is no need to call
> > > > > +  * drm_add_edid_modes() manually in that case.
> >
> > Hm calling drm_add_edid_modes if you have no edid is a bit a funny idea
> > ... Personally I'd just leave out the last sentence, I think that only
> > confuses readers. Or I'm not grasphing what you're trying to tell here.
>
> IIRC, some drivers used and desktop environments expected unknown
> rather than off for LVDS/eDP panels when the lid was shut or if the
> mux was switched to another device in the case of hybrid laptops.

We seem to have totally ditched that in

commit 05c72e77ccda89ff624108b1b59a0fc43843f343
Author: Ville Syrjälä <ville.syrjala at linux.intel.com>
Date:   Tue Jul 17 20:42:14 2018 +0300

    drm/i915: Nuke the LVDS lid notifier

No screaming yet.

But I'm also a bit confused, for a panel there's generally an edid
around, or a fixed (list of) modes. That's enough to stop this
fallback from running, so should be all fine.
-Daniell

>
> Alex
>
>
> >
> > r-b with or without this change since imo super tiny nit.
> >
> > Cheers, Daniel
> >
> > > > > +  *
> > > > >    * Virtual drivers that just want some standard VESA mode with a given
> > > > >    * resolution can call drm_add_modes_noedid(), and mark the preferred
> > > > >    * one using drm_set_preferred_mode().
> > >
> > > --
> > > Regards,
> > >
> > > Laurent Pinchart
> >
> > --
> > Daniel Vetter
> > Software Engineer, Intel Corporation
> > http://blog.ffwll.ch
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel at lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch