[PATCH v2 1/3] ACPI: video: Allow GPU drivers to report no panels

[Mario Limonciello <mario.limonciello@amd.com>]

The current logic for the ACPI backlight detection will create
a backlight device if no native or vendor drivers have created
8 seconds after the system has booted if the ACPI tables
included backlight control methods.

If the GPU drivers have loaded, they may be able to report whether
any LCD panels were found.  Allow using this information to factor
in whether to enable the fallback logic for making an acpi_video0
backlight device.

Suggested-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
---
v1->v2:
 * Cancel registration for backlight device instead (Hans)
 * drop desktop check (Dan)

 drivers/acpi/acpi_video.c | 11 +++++++++++
 include/acpi/video.h      |  1 +
 2 files changed, 12 insertions(+)

diff --git a/drivers/acpi/acpi_video.c b/drivers/acpi/acpi_video.c
index 32953646caeb..f64fdb029090 100644
--- a/drivers/acpi/acpi_video.c
+++ b/drivers/acpi/acpi_video.c
@@ -2178,6 +2178,17 @@ static bool should_check_lcd_flag(void)
 	return false;
 }
 
+/*
+ * At least one graphics driver has reported that no LCD is connected
+ * via the native interface. cancel the registration for fallback acpi_video0.
+ * If another driver still deems this necessary, it can explicitly register it.
+ */
+void acpi_video_report_nolcd(void)
+{
+	cancel_delayed_work(&video_bus_register_backlight_work);
+}
+EXPORT_SYMBOL(acpi_video_report_nolcd);
+
 int acpi_video_register(void)
 {
 	int ret = 0;
diff --git a/include/acpi/video.h b/include/acpi/video.h
index a275c35e5249..1fccb111c197 100644
--- a/include/acpi/video.h
+++ b/include/acpi/video.h
@@ -53,6 +53,7 @@ enum acpi_backlight_type {
 };
 
 #if IS_ENABLED(CONFIG_ACPI_VIDEO)
+extern void acpi_video_report_nolcd(void);
 extern int acpi_video_register(void);
 extern void acpi_video_unregister(void);
 extern void acpi_video_register_backlight(void);
-- 
2.34.1