linux-kernel - Re: [PATCH 1/5] pinctrl: update the documentation for some pinconfig params

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Date:	Sun, 16 Jun 2013 12:26:38 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Heiko Stübner <heiko@...ech.de>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <rob.herring@...xeda.com>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	James Hogan <james.hogan@...tec.com>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>
Subject: Re: [PATCH 1/5] pinctrl: update the documentation for some pinconfig params

On Fri, Jun 14, 2013 at 5:42 PM, Heiko Stübner <heiko@...ech.de> wrote:

> The BIAS_DISABLE and BIAS_HIGH_IMPEDANCE generic pinconfig options were
> missing information about their argument - which should be ignored.
>
> Also the BIAS_PULL_* options may have the pull strength as argument
> when they are activated, while simpler hardware can use any
> non-0 value for it.
>
> Update the kerneldoc to reflect this.
>
> Signed-off-by: Heiko Stuebner <heiko@...ech.de>

I'm holding this patch off.

>   * @PIN_CONFIG_BIAS_PULL_UP: the pin will be pulled up (usually with high
> - *     impedance to VDD). If the argument is != 0 pull-up is enabled,
> - *     if it is 0, pull-up is disabled.
> + *     impedance to VDD). If the argument is != 0 pull-up is enabled. On
> + *     hardware supporting this, the argument should contain the strength of
> + *     the pull in Ohm. If it is 0, pull-up is disabled.

As noted by Laurent, a pull-up of 0 Ohm is a short-circuit (bascially the TOTAL
pull-up) and it is pretty counter-intuitive to have that mean "disable pull-up".
Can we avoid this?

>   * @PIN_CONFIG_BIAS_PULL_DOWN: the pin will be pulled down (usually with high
> - *     impedance to GROUND). If the argument is != 0 pull-down is enabled,
> - *     if it is 0, pull-down is disabled.
> + *     impedance to GROUND). If the argument is != 0 pull-down is enabled. On
> + *     hardware supporting this, the argument should contain the strength of
> + *     the pull in Ohm. If it is 0, pull-down is disabled.

Dito.

>   * @PIN_CONFIG_BIAS_PULL_PIN_DEFAULT: the pin will be pulled up or down based
>   *     on embedded knowledge of the controller, like current mux function.
> - *     If the argument is != 0 pull up/down is enabled, if it is 0,
> - *     the pull is disabled.
> + *     If the argument is != 0 pull up/down is enabled. On hardware supporting
> + *     this, the argument should contain the strength of the pull in Ohm.
> + *     If it is 0, pull is disabled.

Dito.

Can't we rely on PIN_CONFIG_BIAS_DISABLE for all this?

Yours,
Linus Walleij
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