[Intel-gfx] [PATCHv3] drm/i915/display: add support for dual panel backlight

[Arun R Murthy]

The patch with commit 20f85ef89d94 ("drm/i915/backlight: use unique
backlight device names") already adds support for dual panel backlight
but with error prints. Since the patch tried to create the backlight
device with the same name and upon failure will try with a different
name it leads to failure logs in dmesg inturn getting caught by CI.

This patch alternately will check if the backlight class of same name
exists, will use a different name.

v2: reworked on top of the patch commit 20f85ef89d94
("drm/i915/backlight: use unique backlight device names")
v3: fixed the ref count leak(Jani N)

Signed-off-by: Arun R Murthy <arun.r.murthy at intel.com>
---
 .../gpu/drm/i915/display/intel_backlight.c    | 26 +++++++++----------
 1 file changed, 12 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_backlight.c b/drivers/gpu/drm/i915/display/intel_backlight.c
index 110fc98ec280..931446413372 100644
--- a/drivers/gpu/drm/i915/display/intel_backlight.c
+++ b/drivers/gpu/drm/i915/display/intel_backlight.c
@@ -971,26 +971,24 @@ int intel_backlight_device_register(struct intel_connector *connector)
 	if (!name)
 		return -ENOMEM;
 
-	bd = backlight_device_register(name, connector->base.kdev, connector,
-				       &intel_backlight_device_ops, &props);
-
-	/*
-	 * Using the same name independent of the drm device or connector
-	 * prevents registration of multiple backlight devices in the
-	 * driver. However, we need to use the default name for backward
-	 * compatibility. Use unique names for subsequent backlight devices as a
-	 * fallback when the default name already exists.
-	 */
-	if (IS_ERR(bd) && PTR_ERR(bd) == -EEXIST) {
+	bd = backlight_device_get_by_name(name);
+	if (bd) {
+		put_device(&bd->dev);
+		/*
+		 * Using the same name independent of the drm device or connector
+		 * prevents registration of multiple backlight devices in the
+		 * driver. However, we need to use the default name for backward
+		 * compatibility. Use unique names for subsequent backlight devices as a
+		 * fallback when the default name already exists.
+		 */
 		kfree(name);
 		name = kasprintf(GFP_KERNEL, "card%d-%s-backlight",
 				 i915->drm.primary->index, connector->base.name);
 		if (!name)
 			return -ENOMEM;
-
-		bd = backlight_device_register(name, connector->base.kdev, connector,
-					       &intel_backlight_device_ops, &props);
 	}
+	bd = backlight_device_register(name, connector->base.kdev, connector,
+				       &intel_backlight_device_ops, &props);
 
 	if (IS_ERR(bd)) {
 		drm_err(&i915->drm,
-- 
2.25.1