[PATCH] drm/atomic: add quirks for blind save/restore

[Simon Ser <contact@emersion.fr>]

Two quirks to make blind atomic save/restore [1] work correctly:

- Mark the DPMS property as immutable for atomic clients, since
  atomic clients cannot change it.
- Allow user-space to set content protection to "enabled", interpret
  it as "desired".

[1]: https://gitlab.freedesktop.org/wlroots/wlroots/-/merge_requests/3794

Signed-off-by: Simon Ser <contact@emersion.fr>
---

I don't have the motivation to write IGT tests for this.

 drivers/gpu/drm/drm_atomic_uapi.c | 5 +++--
 drivers/gpu/drm/drm_property.c    | 7 +++++++
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_atomic_uapi.c b/drivers/gpu/drm/drm_atomic_uapi.c
index c06d0639d552..95363aac7f69 100644
--- a/drivers/gpu/drm/drm_atomic_uapi.c
+++ b/drivers/gpu/drm/drm_atomic_uapi.c
@@ -741,8 +741,9 @@ static int drm_atomic_connector_set_property(struct drm_connector *connector,
 		state->scaling_mode = val;
 	} else if (property == config->content_protection_property) {
 		if (val == DRM_MODE_CONTENT_PROTECTION_ENABLED) {
-			drm_dbg_kms(dev, "only drivers can set CP Enabled\n");
-			return -EINVAL;
+			/* Degrade ENABLED to DESIRED so that blind atomic
+			 * save/restore works as intended. */
+			val = DRM_MODE_CONTENT_PROTECTION_DESIRED;
 		}
 		state->content_protection = val;
 	} else if (property == config->hdcp_content_type_property) {
diff --git a/drivers/gpu/drm/drm_property.c b/drivers/gpu/drm/drm_property.c
index dfec479830e4..dde42986f8cb 100644
--- a/drivers/gpu/drm/drm_property.c
+++ b/drivers/gpu/drm/drm_property.c
@@ -474,7 +474,14 @@ int drm_mode_getproperty_ioctl(struct drm_device *dev,
 		return -ENOENT;
 
 	strscpy_pad(out_resp->name, property->name, DRM_PROP_NAME_LEN);
+
 	out_resp->flags = property->flags;
+	if (file_priv->atomic && property == dev->mode_config.dpms_property) {
+		/* Quirk: indicate that the legacy DPMS property is not
+		 * writable from atomic user-space, so that blind atomic
+		 * save/restore works as intended. */
+		out_resp->flags |= DRM_MODE_PROP_IMMUTABLE;
+	}
 
 	value_count = property->num_values;
 	values_ptr = u64_to_user_ptr(out_resp->values_ptr);
-- 
2.38.1