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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,
        Nicholas Bishop <nicholasbishop@google.com>,
        Alex Deucher <alexander.deucher@amd.com>
Subject: [PATCH 5.4 28/80] drm/radeon: Fix backlight control on iMac 12,1
Date:   Mon, 21 Feb 2022 09:49:08 +0100
Message-Id: <20220221084916.504044802@linuxfoundation.org>
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From: Nicholas Bishop <nicholasbishop@google.com>

commit 364438fd629f7611a84c8e6d7de91659300f1502 upstream.

The iMac 12,1 does not use the gmux driver for backlight, so the radeon
backlight device is needed to set the brightness.

Bug: https://gitlab.freedesktop.org/drm/amd/-/issues/1838
Signed-off-by: Nicholas Bishop <nicholasbishop@google.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/gpu/drm/radeon/atombios_encoders.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/gpu/drm/radeon/atombios_encoders.c
+++ b/drivers/gpu/drm/radeon/atombios_encoders.c
@@ -197,7 +197,8 @@ void radeon_atom_backlight_init(struct r
 	 * so don't register a backlight device
 	 */
 	if ((rdev->pdev->subsystem_vendor == PCI_VENDOR_ID_APPLE) &&
-	    (rdev->pdev->device == 0x6741))
+	    (rdev->pdev->device == 0x6741) &&
+	    !dmi_match(DMI_PRODUCT_NAME, "iMac12,1"))
 		return;
 
 	if (!radeon_encoder->enc_priv)