[1/5] drm: Add a new connector property for link status

Commit Message

Navare, Manasi Nov. 18, 2016, 7:13 a.m. UTC

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 prune the mode list based
on new information as necessary, set the link status to "bad",
and send a hotplug uevent for userspace to have it re-check the valid modes
through getconnector, and try again. If the theoretical capabilities of the
link can't be reached, the mode list is trimmed based on that.

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.

v4:
* Rebase on drm-nightly
* Add a detailed commit message (Jani Nikula)
v3:
* Drop "link training" from description since this is
not specific to DP (Jani Nikula)
* Add link status member to store property value locally
(Ville Syrjala)
v2:
* Make this a default connector property (Daniel Vetter)

Reviewed-by: Harry Wentland <[e-mail]>
Cc: [e-mail]
Cc: Jani Nikula <[e-mail]>
Cc: Daniel Vetter <[e-mail]>
Cc: Ville Syrjala <[e-mail]>
Cc: Chris Wilson <[e-mail]>
Signed-off-by: Manasi Navare <[e-mail]>
---
 drivers/gpu/drm/drm_connector.c | 17 +++++++++++++++++
 include/drm/drm_connector.h     |  7 ++++++-
 include/drm/drm_mode_config.h   |  5 +++++
 include/uapi/drm/drm_mode.h     |  4 ++++
 4 files changed, 32 insertions(+), 1 deletion(-)

Patch

diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
index b5c6a8e..2b6ee0e 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
@@ -622,6 +632,13 @@  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;
 }
 
diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
index 34f9741..ab564e6 100644
--- a/include/drm/drm_connector.h
+++ b/include/drm/drm_connector.h
@@ -695,6 +695,12 @@  struct drm_connector {
 	uint8_t num_h_tile, num_v_tile;
 	uint8_t tile_h_loc, tile_v_loc;
 	uint16_t tile_h_size, tile_v_size;
+
+	/* Connector Link status
+	 * 0: If the link is Good
+	 * 1: If the link is Bad
+	 */
+	int link_status;
 };
 
 #define obj_to_connector(x) container_of(x, struct drm_connector, base)
@@ -767,7 +773,6 @@  int drm_mode_create_tv_properties(struct drm_device *dev,
 int drm_mode_create_scaling_mode_property(struct drm_device *dev);
 int drm_mode_create_aspect_ratio_property(struct drm_device *dev);
 int drm_mode_create_suggested_offset_properties(struct drm_device *dev);
-
 int drm_mode_connector_set_path_property(struct drm_connector *connector,
 					 const char *path);
 int drm_mode_connector_set_tile_property(struct drm_connector *connector);
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;