[PATCH v4 14/31] drm/radeon: Register ACPI video backlight when skipping radeon backlight registration

Hans de Goede
2022-08-24T12:17:19Z

Typically the acpi_video driver will initialize before radeon, which
used to cause /sys/class/backlight/acpi_video0 to get registered and then
radeon would register its own radeon_bl# device later. After which
the drivers/acpi/video_detect.c code unregistered the acpi_video0 device
to avoid there being 2 backlight devices.

This means that userspace used to briefly see 2 devices and the
disappearing of acpi_video0 after a brief time confuses the systemd
backlight level save/restore code, see e.g.:
https://bbs.archlinux.org/viewtopic.php?id=269920

To fix this the ACPI video code has been modified to make backlight class
device registration a separate step, relying on the drm/kms driver to
ask for the acpi_video backlight registration after it is done setting up
its native backlight device.

Add a call to the new acpi_video_register_backlight() when radeon skips
registering its own backlight device because of e.g. the firmware_flags
or the acpi_video_get_backlight_type() return value. This ensures that
if the acpi_video backlight device should be used, it will be available
before the radeon drm_device gets registered with userspace.

Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
drivers/gpu/drm/radeon/radeon_encoders.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/radeon/radeon_encoders.c b/drivers/gpu/drm/radeon/radeon_encoders.c
index 35c535e48b8d..fbc0a2182318 100644
--- a/drivers/gpu/drm/radeon/radeon_encoders.c
+++ b/drivers/gpu/drm/radeon/radeon_encoders.c
@@ -30,6 +30,8 @@
#include <drm/drm_device.h>
#include <drm/radeon_drm.h>

+#include <acpi/video.h>
+
#include "radeon.h"
#include "radeon_atombios.h"
#include "radeon_legacy_encoders.h"
@@ -167,7 +169,7 @@ static void radeon_encoder_add_backlight(struct radeon_encoder *radeon_encoder,
return;

if (radeon_backlight == 0) {
- return;
+ use_bl = false;
} else if (radeon_backlight == 1) {
use_bl = true;
} else if (radeon_backlight == -1) {
@@ -193,6 +195,13 @@ static void radeon_encoder_add_backlight(struct radeon_encoder *radeon_encoder,
else
radeon_legacy_backlight_init(radeon_encoder, connector);
}
+
+ /*
+ * If there is no native backlight device (which may happen even when
+ * use_bl==true) try registering an ACPI video backlight device instead.
+ */
+ if (!rdev->mode_info.bl_encoder)
+ acpi_video_register_backlight();
}

void
--
2.37.2