This is a note to let you know that I've just added the patch titled
ACPI: video: Fix Apple GMUX backlight detection
to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
acpi-video-fix-apple-gmux-backlight-detection.patch
and it can be found in the queue-6.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 39dffa157c4c787e8bf8919cb8bb0b056e21a5dd
Author: Hans de Goede <hdegoede@xxxxxxxxxx>
Date: Thu Dec 15 10:41:38 2022 +0100
ACPI: video: Fix Apple GMUX backlight detection
[ Upstream commit 3cf3b7f012f3ea8bdc56196e367cf07c10424855 ]
The apple-gmux driver only binds to old GMUX devices which have an
IORESOURCE_IO resource (using inb()/outb()) rather then memory-mapped
IO (IORESOURCE_MEM).
T2 MacBooks use the new style GMUX devices (with IORESOURCE_MEM access),
so these are not supported by the apple-gmux driver. This is not a problem
since they have working ACPI video backlight support.
But the apple_gmux_present() helper only checks if an ACPI device with
the "APP000B" HID is present, causing acpi_video_get_backlight_type()
to return acpi_backlight_apple_gmux disabling the acpi_video backlight
device.
Add a new apple_gmux_backlight_present() helper which checks that
the "APP000B" device actually is an old GMUX device with an IORESOURCE_IO
resource.
This fixes the acpi_video0 backlight no longer registering on T2 MacBooks.
Note people are working to add support for the new style GMUX to Linux:
https://github.com/kekrby/linux-t2/commits/wip/hybrid-graphics
Once this lands this patch should be reverted so that
acpi_video_get_backlight_type() also prefers the gmux on new style GMUX
MacBooks, but for now this is necessary to avoid regressing backlight
control on T2 Macs.
Fixes: 21245df307cb ("ACPI: video: Add Apple GMUX brightness control detection")
Reported-and-tested-by: Aditya Garg <gargaditya08@xxxxxxxx>
Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c
index ffa19d418847..13f10fbcd7f0 100644
--- a/drivers/acpi/video_detect.c
+++ b/drivers/acpi/video_detect.c
@@ -34,6 +34,7 @@
#include <linux/module.h>
#include <linux/pci.h>
#include <linux/platform_data/x86/nvidia-wmi-ec-backlight.h>
+#include <linux/pnp.h>
#include <linux/types.h>
#include <linux/workqueue.h>
#include <acpi/video.h>
@@ -105,6 +106,26 @@ static bool nvidia_wmi_ec_supported(void)
}
#endif
+static bool apple_gmux_backlight_present(void)
+{
+ struct acpi_device *adev;
+ struct device *dev;
+
+ adev = acpi_dev_get_first_match_dev(GMUX_ACPI_HID, NULL, -1);
+ if (!adev)
+ return false;
+
+ dev = acpi_get_first_physical_node(adev);
+ if (!dev)
+ return false;
+
+ /*
+ * drivers/platform/x86/apple-gmux.c only supports old style
+ * Apple GMUX with an IO-resource.
+ */
+ return pnp_get_resource(to_pnp_dev(dev), IORESOURCE_IO, 0) != NULL;
+}
+
/* Force to use vendor driver when the ACPI device is known to be
* buggy */
static int video_detect_force_vendor(const struct dmi_system_id *d)
@@ -755,7 +776,7 @@ static enum acpi_backlight_type __acpi_video_get_backlight_type(bool native)
if (nvidia_wmi_ec_present)
return acpi_backlight_nvidia_wmi_ec;
- if (apple_gmux_present())
+ if (apple_gmux_backlight_present())
return acpi_backlight_apple_gmux;
/* Chromebooks should always prefer native backlight control. */
