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platform/x86: x86-android-tablets: Add a comment about x86_android_tablet_get_gpiod()

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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@redhat.com>
Reviewed-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Link: https://lore.kernel.org/r/20230911210928.264908-1-hdegoede@redhat.com
This commit is contained in:
Hans de Goede
2023-09-11 23:09:28 +02:00
parent 9578db7939
commit eee9cd5d25
1 changed files with 15 additions and 0 deletions
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15
drivers/platform/x86/x86-android-tablets/core.c
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@@ -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)