Commit 3dbc80a3e4c5 ("ACPI: video: Make backlight class device registration a separate step (v2)") combined with commit 5aa9d943e9b6 ("ACPI: video: Don't enable fallback path for creating ACPI backlight by default")

Means that the video.ko code now fully depends on the GPU driver calling acpi_video_register_backlight() for the acpi_video# backlight class devices to get registered.

This means that if the GPU driver does not do this, acpi_backlight=video on the cmdline, or DMI quirks for selecting acpi_video# will not work.

This is a problem on for example Apple iMac14,1 all-in-ones where the monitor's LCD panel shows up as a regular DP connection instead of eDP so the GPU driver will not call acpi_video_register_backlight() [1].

Fix this by making video.ko directly register the acpi_video# devices when these have been explicitly requested either on the cmdline or through DMI quirks (rather then auto-detection being used).

[1] GPU drivers only call acpi_video_register_backlight() when an internal panel is detected, to avoid non working acpi_video# devices getting registered on desktops which unfortunately is a real issue.

Fixes: 5aa9d943e9b6 ("ACPI: video: Don't enable fallback path for creating ACPI backlight by default") Cc: stable@vger.kernel.org Reviewed-by: Mario Limonciello mario.limonciello@amd.com Signed-off-by: Hans de Goede hdegoede@redhat.com --- drivers/acpi/acpi_video.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/drivers/acpi/acpi_video.c b/drivers/acpi/acpi_video.c index 97b711e57bff..c7a6d0b69dab 100644 --- a/drivers/acpi/acpi_video.c +++ b/drivers/acpi/acpi_video.c @@ -1984,6 +1984,7 @@ static int instance; static int acpi_video_bus_add(struct acpi_device *device) { struct acpi_video_bus *video; + bool auto_detect; int error; acpi_status status;

@@ -2045,10 +2046,20 @@ static int acpi_video_bus_add(struct acpi_device *device) mutex_unlock(&video_list_lock);

/* - * The userspace visible backlight_device gets registered separately - * from acpi_video_register_backlight(). + * If backlight-type auto-detection is used then a native backlight may + * show up later and this may change the result from video to native. + * Therefor normally the userspace visible /sys/class/backlight device + * gets registered separately by the GPU driver calling + * acpi_video_register_backlight() when an internal panel is detected. + * Register the backlight now when not using auto-detection, so that + * when the kernel cmdline or DMI-quirks are used the backlight will + * get registered even if acpi_video_register_backlight() is not called. */ acpi_video_run_bcl_for_osi(video); + if (__acpi_video_get_backlight_type(false, &auto_detect) == acpi_backlight_video && + !auto_detect) + acpi_video_bus_register_backlight(video); + acpi_video_bus_add_notify_handler(video);

return 0;