[PATCH v8 05/14] drm: add DRM_CLIENT_CAP_LUMINANCE

[Mario Limonciello <mario.limonciello@amd.com>]

The legacy backlight control interface can only be disabled when both the
client and the driver agree that luminance can be set during a modeset.
Add a DRIVER_CONNECTOR_LUMINANCE driver feature for the driver to
advertise support, and a DRM_CLIENT_CAP_LUMINANCE client capability for
a luminance-aware client to opt in.

When a client sets DRM_CLIENT_CAP_LUMINANCE, every DRM-connected
backlight on the device is marked as taken over; writes to the legacy
/sys/class/backlight/<dev>/brightness attribute then return -EBUSY until
the last luminance-aware client clears the capability or closes its DRM
file. The takeover follows the active backlight_device when
drm_backlight_link() retargets the link.

Signed-off-by: Mario Limonciello (AMD) <superm1@kernel.org>
---
 drivers/gpu/drm/drm_file.c  |  5 +++++
 drivers/gpu/drm/drm_ioctl.c | 24 ++++++++++++++++++++++++
 include/drm/drm_drv.h       |  7 +++++++
 include/drm/drm_file.h      |  8 ++++++++
 include/uapi/drm/drm.h      | 22 ++++++++++++++++++++++
 5 files changed, 66 insertions(+)

diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
index ec820686b3021..4d2520de7614c 100644
--- a/drivers/gpu/drm/drm_file.c
+++ b/drivers/gpu/drm/drm_file.c
@@ -41,6 +41,7 @@
 #include <linux/slab.h>
 #include <linux/vga_switcheroo.h>
 
+#include <drm/drm_backlight.h>
 #include <drm/drm_client_event.h>
 #include <drm/drm_drv.h>
 #include <drm/drm_file.h>
@@ -252,6 +253,10 @@ void drm_file_free(struct drm_file *file)
 	if (drm_core_check_feature(dev, DRIVER_MODESET)) {
 		drm_fb_release(file);
 		drm_property_destroy_user_blobs(dev, file);
+		if (file->supports_luminance_control) {
+			drm_backlight_uninhibit_legacy_all(dev);
+			file->supports_luminance_control = false;
+		}
 	}
 
 	if (drm_core_check_feature(dev, DRIVER_SYNCOBJ))
diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
index 9039a39c43243..de2c9d9ab5285 100644
--- a/drivers/gpu/drm/drm_ioctl.c
+++ b/drivers/gpu/drm/drm_ioctl.c
@@ -28,12 +28,14 @@
  * OTHER DEALINGS IN THE SOFTWARE.
  */
 
+#include "drm/drm.h"
 #include <linux/export.h>
 #include <linux/nospec.h>
 #include <linux/pci.h>
 #include <linux/uaccess.h>
 
 #include <drm/drm_auth.h>
+#include <drm/drm_backlight.h>
 #include <drm/drm_crtc.h>
 #include <drm/drm_drv.h>
 #include <drm/drm_file.h>
@@ -392,6 +394,28 @@ drm_setclientcap(struct drm_device *dev, void *data, struct drm_file *file_priv)
 		file_priv->plane_color_pipeline = req->value;
 		break;
 	}
+	case DRM_CLIENT_CAP_LUMINANCE:
+		if (!drm_core_check_feature(dev, DRIVER_CONNECTOR_LUMINANCE))
+			return -EOPNOTSUPP;
+		if (!file_priv->atomic)
+			return -EINVAL;
+		if (req->value > 1)
+			return -EINVAL;
+
+		/*
+		 * Serialize the compare-and-act so concurrent ioctls on a shared
+		 * fd cannot unbalance the device-wide inhibit count.
+		 */
+		mutex_lock(&dev->mode_config.mutex);
+		if (req->value != file_priv->supports_luminance_control) {
+			if (req->value)
+				drm_backlight_inhibit_legacy_all(dev);
+			else
+				drm_backlight_uninhibit_legacy_all(dev);
+			file_priv->supports_luminance_control = req->value;
+		}
+		mutex_unlock(&dev->mode_config.mutex);
+		break;
 	default:
 		return -EINVAL;
 	}
diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h
index b23830494ed41..449160b9863f6 100644
--- a/include/drm/drm_drv.h
+++ b/include/drm/drm_drv.h
@@ -118,6 +118,13 @@ enum drm_driver_feature {
 	 */
 	DRIVER_CURSOR_HOTSPOT           = BIT(9),
 
+	/**
+	 * @DRIVER_CONNECTOR_LUMINANCE:
+	 *
+	 * Driver supports luminance control on a per connector basis.
+	 */
+	DRIVER_CONNECTOR_LUMINANCE           = BIT(10),
+
 	/* IMPORTANT: Below are all the legacy flags, add new ones above. */
 
 	/**
diff --git a/include/drm/drm_file.h b/include/drm/drm_file.h
index 6ee70ad65e1fd..0bb1e53f36bec 100644
--- a/include/drm/drm_file.h
+++ b/include/drm/drm_file.h
@@ -248,6 +248,14 @@ struct drm_file {
 	 */
 	bool supports_virtualized_cursor_plane;
 
+	/**
+	 * @supports_luminance_control:
+	 *
+	 * This client is capable of setting the luminance for connectors.
+	 *
+	 */
+	bool supports_luminance_control;
+
 	/**
 	 * @master:
 	 *
diff --git a/include/uapi/drm/drm.h b/include/uapi/drm/drm.h
index bc7ef7684099b..a3141d46d7d66 100644
--- a/include/uapi/drm/drm.h
+++ b/include/uapi/drm/drm.h
@@ -903,6 +903,28 @@ struct drm_get_cap {
  */
 #define DRM_CLIENT_CAP_PLANE_COLOR_PIPELINE	7
 
+/**
+ * DRM_CLIENT_CAP_LUMINANCE
+ *
+ * If set to 1, the client declares support for the LUMINANCE connector property
+ * and will control backlight brightness through the DRM atomic interface. This
+ * enables the kernel to expose the LUMINANCE property on connectors that have
+ * an associated backlight device.
+ *
+ * When this capability is enabled:
+ *  - The LUMINANCE property becomes visible on supported connectors
+ *  - Legacy sysfs writes to /sys/class/backlight/{*}/brightness will return
+ *    -EBUSY to prevent conflicts with DRM-based brightness control
+ *  - The client should include luminance values as part of atomic commits
+ *  - Brightness changes are synchronized with display power state (DPMS)
+ *
+ * The LUMINANCE property accepts values from 0 to max_brightness, where 0 turns
+ * off the backlight, and 1 to max_brightness control the brightness level.
+ *
+ * This capability is supported starting in kernel 7.2.
+ */
+#define DRM_CLIENT_CAP_LUMINANCE		8
+
 /* DRM_IOCTL_SET_CLIENT_CAP ioctl argument type */
 struct drm_set_client_cap {
 	__u64 capability;
-- 
2.43.0