Re: [PATCH v4 1/4] drm: Add a new connector atomic property for link status

On Tue, 06 Dec 2016, Manasi Navare manasi.d.navare@intel.com wrote:

At the time userspace does setcrtc, we've already promised the mode would work. The promise is based on the theoretical capabilities of the link, but it's possible we can't reach this in practice. The DP spec describes how the link should be reduced, but we can't reduce the link below the requirements of the mode. Black screen follows.

One idea would be to have setcrtc return a failure. However, it already should not fail as the atomic checks have passed. It would also conflict with the idea of making setcrtc asynchronous in the future, returning before the actual mode setting and link training.

Another idea is to train the link "upfront" at hotplug time, before pruning the mode list, so that we can do the pruning based on practical not theoretical capabilities. However, the changes for link training are pretty drastic, all for the sake of error handling and DP compliance, when the most common happy day scenario is the current approach of link training at mode setting time, using the optimal parameters for the mode. It is also not certain all hardware could do this without the pipe on; not even all our hardware can do this. Some of this can be solved, but not trivially.

Both of the above ideas also fail to address link degradation *during* operation.

The solution is to add a new "link-status" connector property in order to address link training failure in a way that: a) changes the current happy day scenario as little as possible, to avoid regressions, b) can be implemented the same way by all drm drivers, c) is still opt-in for the drivers and userspace, and opting out doesn't regress the user experience, d) doesn't prevent drivers from implementing better or alternate approaches, possibly without userspace involvement. And, of course, handles all the issues presented. In the usual happy day scenario, this is always "good". If something fails during or after a mode set, the kernel driver can set the link status to "bad" and issue a hotplug uevent for userspace to have it re-check the valid modes through GET_CONNECTOR IOCTL, and try modeset again. If the theoretical capabilities of the link can't be reached, the mode list is trimmed based on that.

v4:

• Add comments in kernel-doc format (Daniel Vetter)
• Update the kernel-doc for link-status (Sean Paul)

v3:

• Fixed a build error (Jani Saarinen)

v2:

• Removed connector->link_status (Daniel Vetter)
• Set connector->state->link_status in drm_mode_connector_set_link_status_property

(Daniel Vetter)

• Set the connector_changed flag to true if connector->state->link_status changed.
• Reset link_status to GOOD in update_output_state (Daniel Vetter)
• Never allow userspace to set link status from Good To Bad (Daniel Vetter)

Reviewed-by: Sean Paul seanpaul@chromium.org Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch Acked-by: Tony Cheng tony.cheng@amd.com Acked-by: Harry Wentland harry.wentland@amd.com Cc: Jani Nikula jani.nikula@linux.intel.com Cc: Daniel Vetter daniel.vetter@intel.com Cc: Ville Syrjala ville.syrjala@linux.intel.com Cc: Chris Wilson chris@chris-wilson.co.uk Cc: Sean Paul seanpaul@chromium.org Signed-off-by: Manasi Navare manasi.d.navare@intel.com

---

drivers/gpu/drm/drm_atomic.c | 10 +++++++ drivers/gpu/drm/drm_atomic_helper.c | 15 +++++++++++ drivers/gpu/drm/drm_connector.c | 53 +++++++++++++++++++++++++++++++++++++ include/drm/drm_connector.h | 19 +++++++++++++ include/drm/drm_mode_config.h | 5 ++++ include/uapi/drm/drm_mode.h | 4 +++ 6 files changed, 106 insertions(+)

diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c index 19d7bcb..70a5152 100644 --- a/drivers/gpu/drm/drm_atomic.c +++ b/drivers/gpu/drm/drm_atomic.c @@ -1087,6 +1087,14 @@ int drm_atomic_connector_set_property(struct drm_connector *connector, * now?) atomic writes to DPMS property: */ return -EINVAL;

• } else if (property == config->link_status_property) {

• /* Never downgrade from GOOD to BAD on userspace's request here,
  

•  * only hw issues can do that.
  

•  */
  

• if (state->link_status == DRM_LINK_STATUS_GOOD)
  

• 	return 0;
  

Is it conceivable we'd want to support the userspace requesting the change from GOOD to BAD at a later point in time? If yes, perhaps the right answer here is to return an error on GOOD->BAD transition, so the userspace can distinguish between the kernel rejecting vs. accepting the property set?

BR, Jani.

• state->link_status = val;
  

• return 0;
  

  } else if (connector->funcs->atomic_set_property) { return connector->funcs->atomic_set_property(connector, state, property, val);

@@ -1135,6 +1143,8 @@ static void drm_atomic_connector_print_state(struct drm_printer *p, *val = (state->crtc) ? state->crtc->base.id : 0; } else if (property == config->dpms_property) { *val = connector->dpms;

• } else if (property == config->link_status_property) {

• *val = state->link_status;
  

  } else if (connector->funcs->atomic_get_property) { return connector->funcs->atomic_get_property(connector, state, property, val);

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c index 494680c..3d6c1ce 100644 --- a/drivers/gpu/drm/drm_atomic_helper.c +++ b/drivers/gpu/drm/drm_atomic_helper.c @@ -519,6 +519,13 @@ static int handle_conflicting_encoders(struct drm_atomic_state *state, connector_state); if (ret) return ret;

• if (connector->state->crtc) {
  

• 	crtc_state = drm_atomic_get_existing_crtc_state(state,
  

• 							connector->state->crtc);
  

• 	if (connector->state->link_status !=
  

• 	    connector_state->link_status)
  

• 		crtc_state->connectors_changed = true;
  

• }
  

  }

  /*

@@ -2258,6 +2265,8 @@ static int update_output_state(struct drm_atomic_state *state, NULL); if (ret) return ret;

• 	/* Make sure legacy setCrtc always re-trains */
  

• 	conn_state->link_status = DRM_LINK_STATUS_GOOD;
  

  } }

@@ -2301,6 +2310,12 @@ static int update_output_state(struct drm_atomic_state *state,

• Provides a default crtc set_config handler using the atomic driver interface.

• • NOTE: For backwards compatibility with old userspace this automatically
• • resets the "link-status" property to GOOD, to force any link
• • re-training. The SETCRTC ioctl does not define whether an update does
• • need a full modeset or just a plane update, hence we're allowed to do
• • that. See also drm_mode_connector_set_link_status_property().
• • Returns:
  • Returns 0 on success, negative errno numbers on failure.
  */

diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c index 5a45262..eee038a 100644 --- a/drivers/gpu/drm/drm_connector.c +++ b/drivers/gpu/drm/drm_connector.c @@ -243,6 +243,10 @@ int drm_connector_init(struct drm_device *dev, drm_object_attach_property(&connector->base, config->dpms_property, 0);

• drm_object_attach_property(&connector->base,

• 		   config->link_status_property,
  

• 		   0);
  

• if (drm_core_check_feature(dev, DRIVER_ATOMIC)) { drm_object_attach_property(&connector->base, config->prop_crtc_id, 0); }

@@ -506,6 +510,12 @@ const char *drm_get_subpixel_order_name(enum subpixel_order order) }; DRM_ENUM_NAME_FN(drm_get_dpms_name, drm_dpms_enum_list)

+static const struct drm_prop_enum_list drm_link_status_enum_list[] = {

• { DRM_MODE_LINK_STATUS_GOOD, "Good" },
• { DRM_MODE_LINK_STATUS_BAD, "Bad" },

+}; +DRM_ENUM_NAME_FN(drm_get_link_status_name, drm_link_status_enum_list)

/**

• drm_display_info_set_bus_formats - set the supported bus formats
• @info: display info to store bus formats in

@@ -625,6 +635,11 @@ int drm_display_info_set_bus_formats(struct drm_display_info *info,

• tiling and virtualize both &drm_crtc and &drm_plane if needed. Drivers
• should update this value using drm_mode_connector_set_tile_property().
• Userspace cannot change this property.

• • link-status:

• •  Connector link-status property to indicate the status of link. The default
    

• •  value of link-status is "GOOD". If something fails during or after modeset,
    

• •  the kernel driver may set this to "BAD" and issue a hotplug uevent. Drivers
    

• •  should update this value using drm_mode_connector_set_link_status_property().
    

  • Connectors also have one standardized atomic property:

@@ -666,6 +681,13 @@ int drm_connector_create_standard_properties(struct drm_device *dev) return -ENOMEM; dev->mode_config.tile_property = prop;

• prop = drm_property_create_enum(dev, 0, "link-status",

• 			drm_link_status_enum_list,
  

• 			ARRAY_SIZE(drm_link_status_enum_list));
  

• if (!prop)

• return -ENOMEM;
  

• dev->mode_config.link_status_property = prop;
• return 0;

}

@@ -995,6 +1017,37 @@ 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 link status property of a connector
• • @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
• • may set this link status property to "BAD". The caller then needs to send a
• • hotplug uevent for userspace to re-check the valid modes through
• • GET_CONNECTOR_IOCTL and retry modeset.
• • Note: Drivers cannot rely on userspace to support this property and
• • issue a modeset. As such, they may choose to handle issues (like
• • re-training a link) without userspace's intervention.
• • 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 report any failures in that.
• */

+void drm_mode_connector_set_link_status_property(struct drm_connector *connector,

• 				 uint64_t link_status)
  

+{

• struct drm_device *dev = connector->dev;
• drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
• connector->state->link_status = link_status;
• drm_modeset_unlock(&dev->mode_config.connection_mutex);

+} +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 1218a0c..64e07c5 100644 --- a/include/drm/drm_connector.h +++ b/include/drm/drm_connector.h @@ -90,6 +90,17 @@ enum subpixel_order { };

/**

• • enum drm_link_status - connector's link_status property value
• • This enum is used as the connector's link status property value.
• • It is set to the values defined in uapi.
• */

+enum drm_link_status {

• DRM_LINK_STATUS_GOOD = DRM_MODE_LINK_STATUS_GOOD,
• DRM_LINK_STATUS_BAD = DRM_MODE_LINK_STATUS_BAD,

+};

+/**

• struct drm_display_info - runtime data about the connected sink
• Describes a given display (e.g. CRT or flat panel) and its limitations. For

@@ -213,6 +224,12 @@ struct drm_connector_state {

struct drm_encoder *best_encoder;

• /**

• * @link_status: Connector link_status to keep track of whether link is
  

• * GOOD or BAD to notify userspace if retraining is necessary.
  

• */
  

• enum drm_link_status link_status;
• struct drm_atomic_state *state;

};

@@ -776,6 +793,8 @@ 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); +void drm_mode_connector_set_link_status_property(struct drm_connector *connector,

• 				 uint64_t link_status);
  
  

/**

• struct drm_tile_group - Tile group metadata

diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h index bf9991b..86faee4 100644 --- a/include/drm/drm_mode_config.h +++ b/include/drm/drm_mode_config.h @@ -431,6 +431,11 @@ struct drm_mode_config { */ struct drm_property *tile_property; /**

• * @link_status_property: Default connector property for link status
  

• * of a connector
  

• */
  

• struct drm_property *link_status_property;
• /**
  • @plane_type_property: Default plane property to differentiate
  • CURSOR, PRIMARY and OVERLAY legacy uses of planes.
  */

diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h index 728790b..309c478 100644 --- a/include/uapi/drm/drm_mode.h +++ b/include/uapi/drm/drm_mode.h @@ -123,6 +123,10 @@ #define DRM_MODE_DIRTY_ON 1 #define DRM_MODE_DIRTY_ANNOTATE 2

+/* Link Status options */ +#define DRM_MODE_LINK_STATUS_GOOD 0 +#define DRM_MODE_LINK_STATUS_BAD 1

struct drm_mode_modeinfo { __u32 clock; __u16 hdisplay;