drm/radeon: add a module parameter for backlight control (v2)

Add a module parameter to disable the radeon GPU backlight
controller to override the automatic detection.  Some
laptops seems to indicate that they use the integrated
controller, but appear to actually use an external
controller.

bug:
https://bugs.freedesktop.org/show_bug.cgi?id=81382

v2: fix module parameter description

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

1 files changed, 29 insertions, 8 deletions

diff --git a/drivers/gpu/drm/radeon/radeon_encoders.c b/drivers/gpu/drm/radeon/radeon_encoders.c
index 3c2094c25b53..2a9cd7be9aad 100644
--- a/drivers/gpu/drm/radeon/radeon_encoders.c
+++ b/drivers/gpu/drm/radeon/radeon_encoders.c
@@ -158,10 +158,36 @@ radeon_get_encoder_enum(struct drm_device *dev, uint32_t supported_device, uint8
 	return ret;
 }
 
+static void radeon_encoder_add_backlight(struct radeon_encoder *radeon_encoder,
+					 struct drm_connector *connector)
+{
+	struct drm_device *dev = radeon_encoder->base.dev;
+	struct radeon_device *rdev = dev->dev_private;
+	bool use_bl = false;
+
+	if (!(radeon_encoder->devices & (ATOM_DEVICE_LCD_SUPPORT)))
+		return;
+
+	if (radeon_backlight == 0) {
+		return;
+	} else if (radeon_backlight == 1) {
+		use_bl = true;
+	} else if (radeon_backlight == -1) {
+		use_bl = true;
+	}
+
+	if (use_bl) {
+		if (rdev->is_atom_bios)
+			radeon_atom_backlight_init(radeon_encoder, connector);
+		else
+			radeon_legacy_backlight_init(radeon_encoder, connector);
+		rdev->mode_info.bl_encoder = radeon_encoder;
+	}
+}
+
 void
 radeon_link_encoder_connector(struct drm_device *dev)
 {
-	struct radeon_device *rdev = dev->dev_private;
 	struct drm_connector *connector;
 	struct radeon_connector *radeon_connector;
 	struct drm_encoder *encoder;
@@ -174,13 +200,8 @@ radeon_link_encoder_connector(struct drm_device *dev)
 			radeon_encoder = to_radeon_encoder(encoder);
 			if (radeon_encoder->devices & radeon_connector->devices) {
 				drm_mode_connector_attach_encoder(connector, encoder);
-				if (radeon_encoder->devices & (ATOM_DEVICE_LCD_SUPPORT)) {
-					if (rdev->is_atom_bios)
-						radeon_atom_backlight_init(radeon_encoder, connector);
-					else
-						radeon_legacy_backlight_init(radeon_encoder, connector);
-					rdev->mode_info.bl_encoder = radeon_encoder;
-				}
+				if (radeon_encoder->devices & (ATOM_DEVICE_LCD_SUPPORT))
+					radeon_encoder_add_backlight(radeon_encoder, connector);
 			}
 		}
 	}