Re: [PATCH 1/2] gpio: add pin biasing and drive mode to gpiolib
From: Linus Walleij
Date: Sun Apr 17 2011 - 17:58:24 EST
2011/4/17 Alan Cox <alan@xxxxxxxxxxxxxxxxxxx>:
>> + * enum gpio_drive - drive modes for GPIOs (output)
>> + * @GPIO_DRIVE_PUSH_PULL: the GPIO will be driven actively high and low, this
>> + * is the most typical case and is typically achieved with two active
>> + * transistors on the output
>> + * @GPIO_DRIVE_OPEN_DRAIN: the GPIO will be driven with open drain (open
>> + * collector) which means it is usually wired with other output ports
>> + * which are then pulled up with an external resistor
>> + * @GPIO_DRIVE_OPEN_SOURCE: the GPIO will be driven with open drain
>> + * (open emitter) which is the same as open drain mutatis mutandis but
>> + * pulled to ground
>
> How about "off". As I've pointed out at various times some devices have
> GPIO pins that may or may not be connected depending upon what other chip
> logic is doing.
Sure, why not.
> As I've also noted with various other previous suggestions for API
> additions you also need an "unknown" state so that a device can implement
> the methods but indicate for some pins the value is unknown due to
> hardware or firmware limitations.
OK do you want an unknown biasing mode too, or is "floating" enough
of a default to cover that?
Yours,
Linus Walleij
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