Add a comment explaining why the special x86_android_tablet_get_gpiod() helper is necessary for some of the GPIOs used in the x86-android-tablets; and that for normal GPIO lookups this example should not be followed. Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx> --- drivers/platform/x86/x86-android-tablets/core.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/drivers/platform/x86/x86-android-tablets/core.c b/drivers/platform/x86/x86-android-tablets/core.c index 8a1f22aaac00..b55957bde034 100644 --- a/drivers/platform/x86/x86-android-tablets/core.c +++ b/drivers/platform/x86/x86-android-tablets/core.c @@ -24,6 +24,21 @@ static struct platform_device *x86_android_tablet_device; +/* + * This helper allows getting a gpio_desc *before* the actual device consuming + * the GPIO has been instantiated. This function _must_ only be used to handle + * this special case such as e.g. : + * + * 1. Getting an IRQ from a GPIO for i2c_board_info.irq which is passed to + * i2c_client_new() to instantiate i2c_client-s; or + * 2. Calling desc_to_gpio() to get an old style GPIO number for gpio_keys + * platform_data which still uses old style GPIO numbers. + * + * Since the consuming device has not been instatiated yet a dynamic lookup + * is generated using the special x86_android_tablet dev for dev_id. + * + * For normal GPIO lookups a standard static gpiod_lookup_table _must_ be used. + */ int x86_android_tablet_get_gpiod(const char *chip, int pin, const char *con_id, bool active_low, enum gpiod_flags dflags, struct gpio_desc **desc) -- 2.41.0
