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References: <1303076273-8093-1-git-send-email-linus.walleij@stericsson.com>
	<20110417224816.38ddffee@lxorguk.ukuu.org.uk>
Date: Sun, 17 Apr 2011 23:58:16 +0200
Message-ID: <BANLkTimwbsmQw0Dawz_+LpVf+wU60AbB0g@mail.gmail.com>
Subject: Re: [PATCH 1/2] gpio: add pin biasing and drive mode to gpiolib
From: Linus Walleij <linus.walleij@linaro.org>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Grant Likely <grant.likely@secretlab.ca>, Lee Jones <lee.jones@linaro.org>,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org
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2011/4/17 Alan Cox <alan@lxorguk.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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