linux-kernel - RE: [RFC PATCH v3 2/5] pinctrl: add dt binding support for pinmux mappings

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Message-ID: <74CDBE0F657A3D45AFBB94109FB122FF17801D1DE3@HQMAIL01.nvidia.com>
Date:	Thu, 12 Jan 2012 13:10:04 -0800
From:	Stephen Warren <swarren@...dia.com>
To:	Stephen Warren <swarren@...dia.com>,
	Shawn Guo <shawn.guo@...aro.org>
CC:	Dong Aisheng-B29396 <B29396@...escale.com>,
	Dong Aisheng <dongas86@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linus.walleij@...ricsson.com" <linus.walleij@...ricsson.com>,
	"s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"kernel@...gutronix.de" <kernel@...gutronix.de>,
	"cjb@...top.org" <cjb@...top.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"Simon Glass (sjg@...omium.org)" <sjg@...omium.org>,
	Richard Zhao <richard.zhao@...aro.org>
Subject: RE: [RFC PATCH v3 2/5] pinctrl: add dt binding support for pinmux
 mappings

Stephen Warren wrote at Thursday, January 12, 2012 1:47 PM:
> Shawn Guo wrote at Wednesday, January 11, 2012 8:40 PM:
> > On Wed, Jan 11, 2012 at 10:17:40AM -0800, Stephen Warren wrote:
> ...
> > > So, my position is that:
> > >
> > > * Something (either the pinctrl driver, or the SoC .dtsi file) should
> > > enumerate all available muxable entities that exist in the SoC (pins for
> > > IMX, groups for Tegra).
> >
> > Yes, we enumerate all available pins in pinctrl driver for imx.
> >
> > > * Something (either the pinctrl driver, or the SoC .dtsi file) should
> > > enumerate all the available functions that can be assigned to a muxable
> > > entity.
> >
> > In theory, yes.  But I hope you would agree we do not need to
> > necessarily do this for case like imx.
> 
> Discussing just the Linux driver internals right now; ignoring device
> tree:
> 
> Pinctrl won't let you use a function on a pin/group if that function
> isn't enumerated and doesn't list that pin/group as a valid location
> for that function. Given that, I'm not sure how you can avoid enumerating
> all functions and their legal locations?

Or you can cheat a little:

Define 8 functions named func0, func1, func2, ... func7. Tell pinctrl
that each function is a legal option on every pin. That way, you've
enumerated all the valid functions, and so satisfied pinctrl's error-
checking, yet kept a tiny list of functions. That'd have the bonus side-
effect that the function IDs map very directly to what I assume is in
your HW manuals too!

I wonder if I shouldn't have done that for Tegra. The main reason I didn't
is because the old Tegra pinmux driver didn't.

-- 
nvpublic

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