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

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Daniel,

On Wed, Jun 24, 2020 at 09:23:04AM +0200, Daniel Vetter wrote:
> On Wed, Jun 24, 2020 at 04:12:09AM +0300, Laurent Pinchart wrote:
> > 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@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@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@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.

Sorry, I meant drm_add_modes_noedid(). Is that clearer ?

> r-b with or without this change since imo super tiny nit.
> 
> > > > +	 *
> > > >  	 * 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