linux-kernel - Re: [PATCH 2/7] pinctrl: pinconf-generic: Infer map type from DT property

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Date:	Wed, 12 Nov 2014 10:43:25 -0800
From:	Sören Brinkmann <soren.brinkmann@...inx.com>
To:	Linus Walleij <linus.walleij@...aro.org>
CC:	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Michal Simek <michal.simek@...inx.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Alessandro Rubini <rubini@...pv.it>,
	Heiko Stuebner <heiko@...ech.de>,
	<linux-rockchip@...ts.infradead.org>,
	"linux-sh@...r.kernel.org" <linux-sh@...r.kernel.org>
Subject: Re: [PATCH 2/7] pinctrl: pinconf-generic: Infer map type from DT
 property

On Tue, 2014-11-11 at 01:29PM +0100, Linus Walleij wrote:
> On Wed, Nov 5, 2014 at 2:56 PM, Laurent Pinchart
> <laurent.pinchart@...asonboard.com> wrote:
> > On Monday 03 November 2014 11:05:26 Soren Brinkmann wrote:
> >> With the new 'groups' property, the DT parser can infer the map type
> >> from the fact whether 'pins' or 'groups' is used to specify the pin
> >> group to work on.
> >> To maintain backwards compatibitliy with current usage of the DT
> >> binding, this is only done when an invalid map type is passed to the
> >> parsing function.
> >
> > The Renesas PFC implements similar bindings with using the vendor-specific
> > properties "renesas,pins" and "renesas,groups" (bindings and implementation
> > available at Documentation/devicetree/bindings/pinctrl/renesas,pfc-pinctrl.txt
> > and drivers/pinctrl/sh-pfc/pinctrl.c respectively).
> >
> > The Renesas implementation is a bit more generic in that it allows both pins
> > and groups to be specified in a single subnode. Do you think that feature
> > would make sense for pinconf-generic as well ?
> 
> I think for generic pin controllers either nodes with:
> 
> {
>     function = "foo";
>     pins = "A0", "A1", "A2";
> }
> 
> or
> 
> {
>     function = "foo";
>     groups = "bar", "baz";
> }
> 
> In parsing this it's easy to just look for "function" then see if
> we're mapping to groups or pins.
> 
> It'd be nice if we could then centralize parsing of functions/pins/groups
> and add the non-renesas-prefixed configs as alternatives to genericized
> the bindings, while keeping backward compatibility.

I think the generic parser can't handle that currently. When it finds
'function' it passes the PINs to pinctrl_utils_add_map_mux(). That
function fails when it doesn't receive a group.
I don't know if the non-generic pinctrl drivers solve that somehow, but
pinconf-generic can't handle pins + function in the same node if we
change the meaning of pins to actually just be pins.

That is why I chose the "kludgy" approach. To maintain current behavior.
If nobody needs that though, things could change I guess.

	Sören
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