[Intel-gfx] [PATCH 2/5] drm: Set DRM connector link status property

[Manasi Navare]

On Tue, Nov 15, 2016 at 08:53:27AM +0100, Daniel Vetter wrote:
> On Mon, Nov 14, 2016 at 07:13:20PM -0800, Manasi Navare wrote:
> > In the usual working scenarios, this property is "Good".
> > If something fails during modeset, the DRM driver can
> > set the link status to "Bad", prune the mode list based on the
> > link rate/lane count fallback values and send  hotplug uevent
> > so that userspace that is aware of this property can take an
> > appropriate action by reprobing connectors and re triggering
> > a modeset to improve user experience and avoid black screens.
> > In case of userspace that is not aware of this link status
> > property, the user experience will be unchanged.
> > 
> > The reason for adding the property is to handle link training failures,
> > but it is not limited to DP or link training. For example, if we
> > implement asynchronous setcrtc, we can use this to report any failures
> > in that.
> > 
> > Cc: dri-devel at lists.freedesktop.org
> > Cc: Jani Nikula <jani.nikula at linux.intel.com>
> > Cc: Daniel Vetter <daniel.vetter at intel.com>
> > Cc: Ville Syrjala <ville.syrjala at linux.intel.com>
> > Signed-off-by: Manasi Navare <manasi.d.navare at intel.com>
> 
> One more thing I've forgotten: Just adding the kernel-doc isn't enough
> yet, we need to link this new property into the overall property
> documentations.
> 
> We already have a section "KMS Properties" in
> Documentation/gpu/drm-kms.rst, I think adding a new sub-section called
> "Standard Connector Properties" there with a definition list pointing to
> this function here would be best.
> -Daniel
>

What about other standard proprties like EDID etc? And could you give an
example for writing out a definition list there pointing to this function?
This .rst file currently consists of kernel::doc:: and paths for .h files

Manasi
> > ---
> >  drivers/gpu/drm/drm_connector.c | 38 ++++++++++++++++++++++++++++++++++++++
> >  include/drm/drm_connector.h     |  2 ++
> >  2 files changed, 40 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
> > index d4e852f..09f4093 100644
> > --- a/drivers/gpu/drm/drm_connector.c
> > +++ b/drivers/gpu/drm/drm_connector.c
> > @@ -968,6 +968,44 @@ int drm_mode_connector_update_edid_property(struct drm_connector *connector,
> >  }
> >  EXPORT_SYMBOL(drm_mode_connector_update_edid_property);
> >  
> > +/**
> > + * drm_mode_connector_set_link_status_property - Set the link status property of
> > + * a connector to indicate status of link as a result of link training.
> > + * @connector: drm connector
> > + * @link_status: new value of link status property (0: Good, 1: Bad)
> > + *
> > + * In usual working scenario, this link status property will always be set to
> > + * "GOOD".
> > + * If something fails during or after a mode set, the kernel driver can set this
> > + * link status to "BAD", prune the mode list based on new information and send a
> > + * hotplug uevent for userspace to have it re-check the valid modes through
> > + * Get_connector and try again.
> > + *
> > + * If userspace is not aware of this property, the user experience is the same
> > + * as it currently is. If the userspace is aware of the property, it has a chance
> > + * to improve user experience by handling link training failures, avoiding black
> > + * screens. The DRM driver can chose to not modify property and keep link status
> > + * as "GOOD" always to keep the user experience same as it currently is.
> > + *
> > + * The reason for adding this property is to handle link training failures, but
> > + * it is not limited to DP or link training. For example, if we implement
> > + * asynchronous setcrtc, this property can be used to reportany failures in that.
> > + *
> > + * This function must be called from asynchronous work item.
> > + * Returns zero on success and negative errrno on failure.
> > + */
> > +int drm_mode_connector_set_link_status_property(struct drm_connector *connector,
> > +						uint64_t link_status)
> > +{
> > +	struct drm_device *dev = connector->dev;
> > +
> > +	connector->link_status = link_status;
> > +	return drm_object_property_set_value(&connector->base,
> > +					     dev->mode_config.link_status_property,
> > +					     link_status);
> > +}
> > +EXPORT_SYMBOL(drm_mode_connector_set_link_status_property);
> > +
> >  int drm_mode_connector_set_obj_prop(struct drm_mode_object *obj,
> >  				    struct drm_property *property,
> >  				    uint64_t value)
> > diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> > index ad5c8b0..ac76469 100644
> > --- a/include/drm/drm_connector.h
> > +++ b/include/drm/drm_connector.h
> > @@ -778,6 +778,8 @@ int drm_mode_connector_set_path_property(struct drm_connector *connector,
> >  int drm_mode_connector_set_tile_property(struct drm_connector *connector);
> >  int drm_mode_connector_update_edid_property(struct drm_connector *connector,
> >  					    const struct edid *edid);
> > +int drm_mode_connector_set_link_status_property(struct drm_connector *connector,
> > +						uint64_t link_status);
> >  
> >  /**
> >   * drm_for_each_connector - iterate over all connectors
> > -- 
> > 1.9.1
> > 
> > _______________________________________________
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> > Intel-gfx at lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/intel-gfx
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch