On Tue, 17 May 2022, Hans de Goede <hdegoede@xxxxxxxxxx> wrote: > ATM on x86 laptops where we want userspace to use the acpi_video backlight > device we often register both the GPU's native backlight device and > acpi_video's firmware acpi_video# backlight device. This relies on > userspace preferring firmware type backlight devices over native ones, but > registering 2 backlight devices for a single display really is undesirable. > > On x86 laptops where the native GPU backlight device should be used, > the registering of other backlight devices is avoided by their drivers > using acpi_video_get_backlight_type() and only registering their backlight > if the return value matches their type. > > acpi_video_get_backlight_type() uses > backlight_device_get_by_type(BACKLIGHT_RAW) to determine if a native > driver is available and will never return native if this returns > false. This means that the GPU's native backlight registering code > cannot just call acpi_video_get_backlight_type() to determine if it > should register its backlight, since acpi_video_get_backlight_type() will > never return native until the native backlight has already registered. > > To fix this add a native function parameter to > acpi_video_get_backlight_type(), which when set to true will make > acpi_video_get_backlight_type() behave as if a native backlight has > already been registered. > > Note that all current callers are updated to pass false for the new > parameter, so this change in itself causes no functional changes. > diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c > index becc198e4c22..0a06f0edd298 100644 > --- a/drivers/acpi/video_detect.c > +++ b/drivers/acpi/video_detect.c > @@ -17,12 +17,14 @@ > * Otherwise vendor specific drivers like thinkpad_acpi, asus-laptop, > * sony_acpi,... can take care about backlight brightness. > * > - * Backlight drivers can use acpi_video_get_backlight_type() to determine > - * which driver should handle the backlight. > + * Backlight drivers can use acpi_video_get_backlight_type() to determine which > + * driver should handle the backlight. RAW/GPU-driver backlight drivers must > + * pass true for the native function argument, other drivers must pass false. > * > * If CONFIG_ACPI_VIDEO is neither set as "compiled in" (y) nor as a module (m) > * this file will not be compiled and acpi_video_get_backlight_type() will > - * always return acpi_backlight_vendor. > + * return acpi_backlight_native when its native argument is true and > + * acpi_backlight_vendor when it is false. > */ Frankly, I think the boolean native parameter here, and at the call sites, is confusing, and the slightly different explanations in the commit message and comment here aren't helping. I suggest adding a separate function that the native backlight drivers should use. I think it's more obvious all around, and easier to document too. BR, Jani. -- Jani Nikula, Intel Open Source Graphics Center
