linux-kernel - Re: [PATCH 1/2] gpio: add pin biasing and drive mode to gpiolib

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Date:	Sun, 17 Apr 2011 23:58:16 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Grant Likely <grant.likely@...retlab.ca>,
	Lee Jones <lee.jones@...aro.org>, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/2] gpio: add pin biasing and drive mode to gpiolib

2011/4/17 Alan Cox <alan@...rguk.ukuu.org.uk>:

>> + * 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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