Merge tag 'acpi-6.11-rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm

Pull ACPI fix from Rafael Wysocki:
 "Fix backlight control on a Dell All In One system where a backlight
  controller board is attached to a UART port and the dell-uart
  backlight driver binds to it, but the backlight is actually controlled
  by other means (Hans de Goede)"

* tag 'acpi-6.11-rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm:
  ACPI: video: Add backlight=native quirk for Dell OptiPlex 7760 AIO
  platform/x86: dell-uart-backlight: Use acpi_video_get_backlight_type()
  ACPI: video: Add Dell UART backlight controller detection

Author: torvalds

drivers/acpi/video_detect.c

@@ -54,6 +54,8 @@ static void acpi_video_parse_cmdline(void)
 		acpi_backlight_cmdline = acpi_backlight_nvidia_wmi_ec;
 	if (!strcmp("apple_gmux", acpi_video_backlight_string))
 		acpi_backlight_cmdline = acpi_backlight_apple_gmux;
+	if (!strcmp("dell_uart", acpi_video_backlight_string))
+		acpi_backlight_cmdline = acpi_backlight_dell_uart;
 	if (!strcmp("none", acpi_video_backlight_string))
 		acpi_backlight_cmdline = acpi_backlight_none;
 }
@@ -821,6 +823,21 @@ static const struct dmi_system_id video_detect_dmi_table[] = {
 		},
 	},
 
+	/*
+	 * Dell AIO (All in Ones) which advertise an UART attached backlight
+	 * controller board in their ACPI tables (and may even have one), but
+	 * which need native backlight control nevertheless.
+	 */
+	{
+	 /* https://bugzilla.redhat.com/show_bug.cgi?id=2303936 */
+	 .callback = video_detect_force_native,
+	 /* Dell OptiPlex 7760 AIO */
+	 .matches = {
+		DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
+		DMI_MATCH(DMI_PRODUCT_NAME, "OptiPlex 7760 AIO"),
+		},
+	},
+
 	/*
 	 * Models which have nvidia-ec-wmi support, but should not use it.
 	 * Note this indicates a likely firmware bug on these models and should
@@ -918,6 +935,7 @@ enum acpi_backlight_type __acpi_video_get_backlight_type(bool native, bool *auto
 	static DEFINE_MUTEX(init_mutex);
 	static bool nvidia_wmi_ec_present;
 	static bool apple_gmux_present;
+	static bool dell_uart_present;
 	static bool native_available;
 	static bool init_done;
 	static long video_caps;
@@ -932,6 +950,7 @@ enum acpi_backlight_type __acpi_video_get_backlight_type(bool native, bool *auto
 				    &video_caps, NULL);
 		nvidia_wmi_ec_present = nvidia_wmi_ec_supported();
 		apple_gmux_present = apple_gmux_detect(NULL, NULL);
+		dell_uart_present = acpi_dev_present("DELL0501", NULL, -1);
 		init_done = true;
 	}
 	if (native)
@@ -962,6 +981,9 @@ enum acpi_backlight_type __acpi_video_get_backlight_type(bool native, bool *auto
 	if (apple_gmux_present)
 		return acpi_backlight_apple_gmux;
 
+	if (dell_uart_present)
+		return acpi_backlight_dell_uart;
+
 	/* Use ACPI video if available, except when native should be preferred. */
 	if ((video_caps & ACPI_VIDEO_BACKLIGHT) &&
 	     !(native_available && prefer_native_over_acpi_video()))

drivers/platform/x86/dell/Kconfig

@@ -161,6 +161,7 @@ config DELL_SMO8800
 config DELL_UART_BACKLIGHT
 	tristate "Dell AIO UART Backlight driver"
 	depends on ACPI
+	depends on ACPI_VIDEO
 	depends on BACKLIGHT_CLASS_DEVICE
 	depends on SERIAL_DEV_BUS
 	help

drivers/platform/x86/dell/dell-uart-backlight.c

@@ -20,6 +20,7 @@
 #include <linux/string.h>
 #include <linux/types.h>
 #include <linux/wait.h>
+#include <acpi/video.h>
 #include "../serdev_helpers.h"
 
 /* The backlight controller must respond within 1 second */
@@ -332,10 +333,17 @@ struct serdev_device_driver dell_uart_bl_serdev_driver = {
 
 static int dell_uart_bl_pdev_probe(struct platform_device *pdev)
 {
+	enum acpi_backlight_type bl_type;
 	struct serdev_device *serdev;
 	struct device *ctrl_dev;
 	int ret;
 
+	bl_type = acpi_video_get_backlight_type();
+	if (bl_type != acpi_backlight_dell_uart) {
+		dev_dbg(&pdev->dev, "Not loading (ACPI backlight type = %d)\n", bl_type);
+		return -ENODEV;
+	}
+
 	ctrl_dev = get_serdev_controller("DELL0501", NULL, 0, "serial0");
 	if (IS_ERR(ctrl_dev))
 		return PTR_ERR(ctrl_dev);

include/acpi/video.h

@@ -50,6 +50,7 @@ enum acpi_backlight_type {
 	acpi_backlight_native,
 	acpi_backlight_nvidia_wmi_ec,
 	acpi_backlight_apple_gmux,
+	acpi_backlight_dell_uart,
 };
 
 #if IS_ENABLED(CONFIG_ACPI_VIDEO)