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

[Daniel Vetter]

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

> ---
>  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