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

[Daniel Vetter]

On Mon, Nov 14, 2016 at 07:23:33PM -0800, Manasi Navare wrote:
> None of the other functions that set the connector property hold the 
> mode config locks while setting the connector property, I am following
> the same convention.
> Also we dont need to grab and release the locks in i915_modeset_work_func
> that first validates the modes and then sets this link status property.

Which other functions don't hold the mode_config.mutex?
-Daniel

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