linux-kernel - Re: [RESEND PATCH 1/2] pinctrl: change function behavior for per pin muxing controllers

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Message-ID: <557EF60D.8020007@wwwdotorg.org>
Date:	Mon, 15 Jun 2015 09:58:05 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Ludovic Desroches <ludovic.desroches@...el.com>,
	linux-arm-kernel@...ts.infradead.org, linux-gpio@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
CC:	linus.walleij@...aro.org, nicolas.ferre@...el.com
Subject: Re: [RESEND PATCH 1/2] pinctrl: change function behavior for per
 pin muxing controllers

On 06/10/2015 09:04 AM, Ludovic Desroches wrote:
> When having a controller which allows per pin muxing, declaring with
> which groups a function can be used is a useless constraint since groups
> are something virtual.

This isn't true.

Irrespective of whether a particular piece of pinmux HW can control the 
mux function for each pin individually, or only in groups, it's quite 
likely that each function can only be selected onto a subset of those 
pins or groups. Requiring the pinctrl driver to inform the core which 
set of pins/groups particular functions can be selected onto seems quite 
reasonable.

In my opinion at least, for HW that can select the mux function at the 
per-pin level, the only sensible set of groups is one group per pin with 
each group containing a single pin. Any other use of groups is a 
SW/user-level construct, and is something unrelated to why the pinctrl 
subsystem supports groups. If we want to represent those groups in 
pinctrl, there should be two separate sets of groups; one to represent 
the actual HW capabilities, and one to represent the SW/user-level 
convenience abstractions.
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