linux-kernel - Re: [PATCH] GPIOLIB: add generic gpio_set

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Date:	Tue, 9 Aug 2011 12:04:06 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Grant Likely <grant.likely@...retlab.ca>
Cc:	Paul Mundt <lethal@...ux-sh.org>,
	Linus Walleij <linus.walleij@...ricsson.com>,
	Barry Song <Baohua.Song@....com>, workgroup.linux@....com,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] GPIOLIB: add generic gpio_set_pull API

On Mon, Aug 8, 2011 at 8:24 PM, Grant Likely <grant.likely@...retlab.ca> wrote:
> On Mon, Aug 8, 2011 at 2:15 AM, Paul Mundt <lethal@...ux-sh.org> wrote:
>> On Sun, Aug 07, 2011 at 10:19:33PM -0700, Barry Song wrote:
>>> Now there are many different implementations for GPIO pull configuration, for
>>> example:
>>> s3c_gpio_setpull()
>>> tegra_pinmux_set_pullupdown()
>>> chipcHw_setPinPullup()
>>> gpio_pullup()
>>> s3c2410_gpio_pullup()
>>>
>>> This patch adds a new generic gpio_set_pull API so that all SoCs can have unified
>>> codes.
>>>
>>> Signed-off-by: Barry Song <Baohua.Song@....com>
>>
>> For arch/arm/mach-shmobile we also have gpio_pull_up() for board-g4evm.c
>> and gpio_pull_down() for board-mackerel.c. Both of these would benefit
>> from this sort of an API addition.
>
> I think I'm okay with this API change.  Linus, what say you?  How does
> this interact with your plans for pinctrl?

I have already proposed a similar mechanism in the past, so let's
recap:

1.First I proposed to expose gpio_to_chip() so each driver could
  provide any custom functions using foo_gpio_set_foo() or so
  by dereferencing the struct gpio_chip.
  NIXED: due to bad experience with doing exactly this for
  IRQ chips (Grant)

2. Second I added a sort-of generic control function;
   gpio_config() which would sit in gpiolib and take an enum
   for each operation, if one of these would be
   GPIO_SET_PULL, and a second argument would be
   whether to pull it up or down or open collector or
   open drain or schmitt-trigger or whatever. As you see
   the problem is not limited to up/down.
   This is equal to the proposed patch but with two
   arguments and broader scope, can also be used
   for drive strength etc.

3. Alan Cox suggested that we use a more generic
   control function instead so I wrapped it to an ioctl()-
   like operation with an opaque argument instead.
   This is especially good when you need to pass
   data *out* of the function, not just *in*.

4. After talks with Grant I submitted (1) again.

I'm basically happy with anything as long as there is some
progress, right now we're only bikeshedding, so I'm, resting
my case.

Linus Walleij
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