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.deuc...@amd.com> Signed-off-by: Hans de Goede <hdego...@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
