linux-kernel - [PATCH] drm/radeon: initialize atom DIG backlight for iMac12,1 and iMac12,2 with Radeon 6750M

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Date: Wed, 15 May 2024 15:20:09 -0400
From: Kendall Smith <kendallsm2@...oud.com>
To: amd-gfx@...ts.freedesktop.org
Cc: linux-kernel@...r.kernel.org,
	Kendall Smith <kendallsm2@...oud.com>
Subject: [PATCH] drm/radeon: initialize atom DIG backlight for iMac12,1 and iMac12,2 with Radeon 6750M

If a Radeon 6750M GPU from an iMac12,1 is installed into an iMac 12,2, there is no backlight device initialized during boot. Everything else is functional, but the display brightness cannot be controlled. There are no directories present in /sys/class/backlight after booting. A simple one line modification to an if statement fixes this issue by initializing the radeon backlight device for an iMac12,2 as well if it has a 6750M. After the patch, brightness can be controlled and radeon_bl0 is present in /sys/class/backlight. This was tested by compiling the latest kernel with and without the patch.

Signed-off-by: Kendall Smith <kendallsm2@...oud.com>
---
 drivers/gpu/drm/radeon/atombios_encoders.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/radeon/atombios_encoders.c b/drivers/gpu/drm/radeon/atombios_encoders.c
index 2bff0d9e20f5..7b11674f5d45 100644
--- a/drivers/gpu/drm/radeon/atombios_encoders.c
+++ b/drivers/gpu/drm/radeon/atombios_encoders.c
@@ -201,7 +201,7 @@ void radeon_atom_backlight_init(struct radeon_encoder *radeon_encoder,
 	 */
 	if ((rdev->pdev->subsystem_vendor == PCI_VENDOR_ID_APPLE) &&
 	    (rdev->pdev->device == 0x6741) &&
-	    !dmi_match(DMI_PRODUCT_NAME, "iMac12,1"))
+	    !(dmi_match(DMI_PRODUCT_NAME, "iMac12,1") || dmi_match(DMI_PRODUCT_NAME, "iMac12,2")))
 		return;

 	if (!radeon_encoder->enc_priv)
-- 
2.34.1