Hi, On 5/18/22 10:55, Jani Nikula wrote: > 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. Can you elaborate the "slightly different explanations in the commit message and comment" part a bit (so that I can fix this) ? > 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. Code wise I think this would mean renaming the original and then adding 2 wrappers, but that is fine with me. I've no real preference either way and I'm happy with adding a new variant of acpi_video_get_backlight_type() for the native backlight drivers any suggestion for a name ? Regards, Hans
