linux-kernel - Re: [PATCH 2/5] pinctrl: clarify some dt pinconfig options

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Date:	Wed, 19 Jun 2013 16:10:39 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Heiko Stübner <heiko@...ech.de>
CC:	Linus Walleij <linus.walleij@...aro.org>,
	"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@...xeda.com, devicetree-discuss@...ts.ozlabs.org,
	James Hogan <james.hogan@...tec.com>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>
Subject: Re: [PATCH 2/5] pinctrl: clarify some dt pinconfig options

On 06/14/2013 09:42 AM, Heiko Stübner wrote:
> The bias-pull-* options use values > 0 to indicate that the pull should
> be activated and optionally also indicate the strength of the pull.
> Therefore use an default value of 1 for these options.
> 
> Split the low-power-mode option into low-power-enable and -disable.
> 
> Update the documentation to describe the param arguments better.
> 
> Wrong default options
> Reported-by: James Hogan <james.hogan@...tec.com>
> 

That blank line should be before the Reported-by not after it.

> Signed-off-by: Heiko Stuebner <heiko@...ech.de>

> diff --git a/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt b/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt

> -low-power-mode		- low power mode
> +low-power-enable	- enable low power mode
> +low-power-disable	- disable low power mode

Hmmm. That's changing the binding definition. What if somebody already
wrote their device tree according previous definition?

It seems to be that tri-states are preferable for pinctrl DT:

no entry: do nothing
= 0: disable
= 1: enable

> +Arguments for parameters:
> +
> +- bias-pull-up, -down and -pin-default take as optional argument 0 to disable
> +  the pull, on hardware supporting it the pull strength in Ohm. bias-disable
> +  will also disable any active pull.

Does this agree with the latest definition of the kernel-internal
meaning of 0 for pull-up/down?

> +- input-schmitt takes as argument the adjustable hysteresis in a
> +  driver-specific format
> +
> +- input-debounce takes the debounce time as argument or 0 to disable debouncing
> +
> +- power-source argument is the custom value describing the source to select
> +
> +- slew-rate takes as argument the target rate in a driver-specific format

If those things have driver-specific (note: should be
DT-binding-specific, not driver-specific) values, then I'm not convinced
that having a generic parameter name for them is a good idea; it makes
things look the same when they aren't. By forcing each binding to
include the vendor prefix on those properties and hence define a custom
property name, you're making it clear that the semantics may be different.
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