linux-kernel - Re: [PATCH] pinctrl: document the "GPIO mode" pitfall

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Date:	Mon, 13 May 2013 01:36:23 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:	Linus Walleij <linus.walleij@...ricsson.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Stephen Warren <swarren@...dia.com>,
	Anmar Oueja <anmar.oueja@...aro.org>,
	Pankaj Dev <pankaj.dev@...com>
Subject: Re: [PATCH] pinctrl: document the "GPIO mode" pitfall

On Sat, Apr 27, 2013 at 3:16 AM, Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
> On Friday 26 April 2013 10:49:12 Linus Walleij wrote:

>> > Does DRIVE_* imply that the pin is driven by the selected function, and
>> > OUTPUT imply that the pin is driven to a fixed level ?
>>
>> That is unclear, but I suggest DRIVE* implies that everything on the pin
>> is driven according to that configuration. (Else it is getting ignored...)
>>
>> OUTPUT would be used when you don't know the particulars or when
>> the driving cannot be controlled in a fine-grained manner like with the
>> DRIVE* configs.
>>
>> Does this make sense?
>
> Kinda, but it's still unclear to me. While the options are (briefly)
> documented, how they interact isn't.

Do you think the sematics need to be etched in stone or do
you think it could be left as driver-specific, like if I write in the
defintion that the interaction of different config arguments is up
to the driver?

>> > What about cases where I want to drive the pin to a fixed level in a non
>> > low-power output mode (for instance because I need more current that what
>> > the low-power output mode provides) ?
>>
>> Just use pinconfig for that?
>
> How would you do so ? Only OUTPUT allows setting the output level explictly,
> the other DRIVE_* options don't specify the output level.

The PIN_CONFIG_DRIVE_STRENGTH argument is in mA.

Is this what you're after or something else?

Yours,
Linus Walleij
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