Hi, On 5/19/22 11:02, Jani Nikula wrote: > On Wed, 18 May 2022, Hans de Goede <hdegoede@xxxxxxxxxx> wrote: >> 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. > > Regarding the question below, this is the part that throws me off. > >>>> >>>> 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 ? > > Alternatively, do the native backlight drivers have any need for the > actual backlight type information from acpi? They only need to be able > to ask if they should register themselves, right? > > I understand this sounds like bikeshedding, but I'm trying to avoid > duplicating the conditions in the drivers where a single predicate > function call could be sufficient, and the complexity could be hidden in > acpi. > > if (!acpi_video_backlight_use_native()) > return; acpi_video_backlight_use_native() sounds good, I like I will change this for v2. This also removes churn in all the other acpi_video_get_backlight_type() callers. > Perhaps all the drivers/platform/x86/* backlight drivers could use: > > if (acpi_video_backlight_use_vendor()) > ... Hmm, as part of the ractoring there also will be new apple_gmux and nvidia_wmi_ec types. I'm not sure about adding seperate functions for all of those vs get_type() != foo. I like get_type != foo because it makes clear that there will also be another caller somewhere where get_type == foo and that that one will rbe the one which actually gets to register its backlight. > You can still use the native parameter etc. internally, but just hide > the details from everyone else, and, hopefully, make it harder for them > to do silly things? Ack. Regards, Hans
