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

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Date:	Wed, 20 Apr 2011 23:04:35 +0800
From:	Haojian Zhuang <haojian.zhuang@...il.com>
To:	Kyungmin Park <kmpark@...radead.org>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Ben Nizette <bn@...sdigital.com>,
	Linus Walleij <linus.walleij@...ricsson.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	linux-kernel@...r.kernel.org,
	Grant Likely <grant.likely@...retlab.ca>,
	Lee Jones <lee.jones@...aro.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/2] gpio: add pin biasing and drive mode to gpiolib

On Wed, Apr 20, 2011 at 10:40 PM, Kyungmin Park <kmpark@...radead.org> wrote:
> On Wed, Apr 20, 2011 at 11:26 PM, Haojian Zhuang
> <haojian.zhuang@...il.com> wrote:
>> On Tue, Apr 19, 2011 at 4:51 PM, Kyungmin Park <kmpark@...radead.org> wrote:
>>>>
>>>> Leaving aside the current input/output and on/off bits I would go for
>>>> being able to do
>>>>
>>>>        gpio_get_property(gpio, GPIO_BIAS, GPIO_BIAS_WHATEVER);
>>>>        gpio_set_property(gpio, GPIO_BIAS, GPIO_BIAS_WHATEVER_ELSE);
>>>
>>> One more consideration, not mentioned previous time, is that pin
>>> configuration for power down mode.
>>> Samsung SoCs has retention GPIO configurations at sleep (suspend)
>>> mode. and restore it at resume time.
>>> it's need to reduce power and proper operation after suspend.
>>>
>> I have a little confusion. In ARM SoC, a lot of pins are used as
>> multi-functions.
>>
>> Before suspend, it may be configured as some function that isn't GPIO.
>> Is it a goal
>> that avoid declaring gpio_request() for suspend and updating the setting of pin?
>
> E.g., When WiFi is turn on and system goes the sleep, wifi should be
> turn on. For this it should be configure the power down gpio
> configuration properly. Its' different that call the gpio_set_value
> function.
>
> One more, even though some pins are used for other purpose instead of
> GPIO. It needs to be configure as input or output at power down mode
> registers.
>
> Thank you,
> Kyungmin Park
>
I have an another question on board initialization. The configuration on pins
are including drive strength, pull and multiple function.

Since this patch can configure drive strength, pull. Will it be preferred to use
in board initialization?
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