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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Arun R Murthy <arun.r.murthy@intel.com>,
        Jani Nikula <jani.nikula@intel.com>,
        Rodrigo Vivi <rodrigo.vivi@intel.com>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.15 012/107] drm/i915/display: avoid warnings when registering dual panel backlight
Date:   Tue,  6 Sep 2022 15:29:53 +0200
Message-Id: <20220906132822.278140983@linuxfoundation.org>
In-Reply-To: <20220906132821.713989422@linuxfoundation.org>
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From: Arun R Murthy <arun.r.murthy@intel.com>

[ Upstream commit 868e8e5156a1f8d92ca83fdbac6fd52798650792 ]

Commit 20f85ef89d94 ("drm/i915/backlight: use unique backlight device
names") added support for multiple backlight devices on dual panel
systems, but did so with error handling on -EEXIST from
backlight_device_register(). Unfortunately, that triggered a warning in
dmesg all the way down from sysfs_add_file_mode_ns() and
sysfs_warn_dup().

Instead of optimistically always attempting to register with the default
name ("intel_backlight", which we have to retain for backward
compatibility), check if a backlight device with the name exists first,
and, if so, use the card and connector based 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)

Fixes: 20f85ef89d94 ("drm/i915/backlight: use unique backlight device names")
Signed-off-by: Arun R Murthy <arun.r.murthy@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220808035750.3111046-1-arun.r.murthy@intel.com
(cherry picked from commit 4234ea30051200fc6016de10e4d58369e60b38f1)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 .../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 4b0086ee48519..60f91ac7d1427 100644
--- a/drivers/gpu/drm/i915/display/intel_backlight.c
+++ b/drivers/gpu/drm/i915/display/intel_backlight.c
@@ -966,26 +966,24 @@ 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,
-- 
2.35.1