drm: Add Content Protection property

This patch adds a new optional connector property to allow userspace to enable
protection over the content it is displaying. This will typically be implemented
by the driver using HDCP.

The property is a tri-state with the following values:
- OFF: Self explanatory, no content protection
- DESIRED: Userspace requests that the driver enable protection
- ENABLED: Once the driver has authenticated the link, it sets this value

The driver is responsible for downgrading ENABLED to DESIRED if the link becomes
unprotected. The driver should also maintain the desiredness of protection
across hotplug/dpms/suspend.

If this looks familiar, I posted [1] this 3 years ago. We have been using this
in ChromeOS across exynos, mediatek, and rockchip over that time.

Changes in v2:
 - Pimp kerneldoc for content_protection_property (Daniel)
 - Drop sysfs attribute
Changes in v3:
 - None
Changes in v4:
- Changed kerneldoc to recommend userspace polling (Daniel)
- Changed kerneldoc to briefly describe how to attach the property (Daniel)
Changes in v5:
- checkpatch whitespace noise
- Change DRM_MODE_CONTENT_PROTECTION_OFF to DRM_MODE_CONTENT_PROTECTION_UNDESIRED
Changes in v6:
- None

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Sean Paul <seanpaul@chromium.org>

[1] https://lists.freedesktop.org/archives/dri-devel/2014-December/073336.html
Link: https://patchwork.freedesktop.org/patch/msgid/20180108195545.218615-4-seanpaul@chromium.org

1 files changed, 78 insertions, 0 deletions

diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
index 2559c615d984..b85a7749709d 100644
--- a/drivers/gpu/drm/drm_connector.c
+++ b/drivers/gpu/drm/drm_connector.c
@@ -756,6 +756,13 @@ static const struct drm_prop_enum_list drm_tv_subconnector_enum_list[] = {
 DRM_ENUM_NAME_FN(drm_get_tv_subconnector_name,
 		 drm_tv_subconnector_enum_list)
 
+static struct drm_prop_enum_list drm_cp_enum_list[] = {
+	{ DRM_MODE_CONTENT_PROTECTION_UNDESIRED, "Undesired" },
+	{ DRM_MODE_CONTENT_PROTECTION_DESIRED, "Desired" },
+	{ DRM_MODE_CONTENT_PROTECTION_ENABLED, "Enabled" },
+};
+DRM_ENUM_NAME_FN(drm_get_content_protection_name, drm_cp_enum_list)
+
 /**
  * DOC: standard connector properties
  *
@@ -826,6 +833,41 @@ DRM_ENUM_NAME_FN(drm_get_tv_subconnector_name,
  * 	Indicates the output should be ignored for purposes of displaying a
  * 	standard desktop environment or console. This is most likely because
  * 	the output device is not rectilinear.
+ * Content Protection:
+ *	This property is used by userspace to request the kernel protect future
+ *	content communicated over the link. When requested, kernel will apply
+ *	the appropriate means of protection (most often HDCP), and use the
+ *	property to tell userspace the protection is active.
+ *
+ *	Drivers can set this up by calling
+ *	drm_connector_attach_content_protection_property() on initialization.
+ *
+ *	The value of this property can be one of the following:
+ *
+ *	- DRM_MODE_CONTENT_PROTECTION_UNDESIRED = 0
+ *		The link is not protected, content is transmitted in the clear.
+ *	- DRM_MODE_CONTENT_PROTECTION_DESIRED = 1
+ *		Userspace has requested content protection, but the link is not
+ *		currently protected. When in this state, kernel should enable
+ *		Content Protection as soon as possible.
+ *	- DRM_MODE_CONTENT_PROTECTION_ENABLED = 2
+ *		Userspace has requested content protection, and the link is
+ *		protected. Only the driver can set the property to this value.
+ *		If userspace attempts to set to ENABLED, kernel will return
+ *		-EINVAL.
+ *
+ *	A few guidelines:
+ *
+ *	- DESIRED state should be preserved until userspace de-asserts it by
+ *	  setting the property to UNDESIRED. This means ENABLED should only
+ *	  transition to UNDESIRED when the user explicitly requests it.
+ *	- If the state is DESIRED, kernel should attempt to re-authenticate the
+ *	  link whenever possible. This includes across disable/enable, dpms,
+ *	  hotplug, downstream device changes, link status failures, etc..
+ *	- Userspace is responsible for polling the property to determine when
+ *	  the value transitions from ENABLED to DESIRED. This signifies the link
+ *	  is no longer protected and userspace should take appropriate action
+ *	  (whatever that might be).
  *
  * Connectors also have one standardized atomic property:
  *
@@ -1127,6 +1169,42 @@ int drm_connector_attach_scaling_mode_property(struct drm_connector *connector,
 EXPORT_SYMBOL(drm_connector_attach_scaling_mode_property);
 
 /**
+ * drm_connector_attach_content_protection_property - attach content protection
+ * property
+ *
+ * @connector: connector to attach CP property on.
+ *
+ * This is used to add support for content protection on select connectors.
+ * Content Protection is intentionally vague to allow for different underlying
+ * technologies, however it is most implemented by HDCP.
+ *
+ * The content protection will be set to &drm_connector_state.content_protection
+ *
+ * Returns:
+ * Zero on success, negative errno on failure.
+ */
+int drm_connector_attach_content_protection_property(
+		struct drm_connector *connector)
+{
+	struct drm_device *dev = connector->dev;
+	struct drm_property *prop;
+
+	prop = drm_property_create_enum(dev, 0, "Content Protection",
+					drm_cp_enum_list,
+					ARRAY_SIZE(drm_cp_enum_list));
+	if (!prop)
+		return -ENOMEM;
+
+	drm_object_attach_property(&connector->base, prop,
+				   DRM_MODE_CONTENT_PROTECTION_UNDESIRED);
+
+	connector->content_protection_property = prop;
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_connector_attach_content_protection_property);
+
+/**
  * drm_mode_create_aspect_ratio_property - create aspect ratio property
  * @dev: DRM device
  *