linux-kernel - Re: Pinmux bindings proposal V2

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Date:	Fri, 27 Jan 2012 09:37:32 -0800
From:	Tony Lindgren <tony@...mide.com>
To:	Simon Glass <sjg@...omium.org>
Cc:	Stephen Warren <swarren@...dia.com>,
	Dong Aisheng-B29396 <B29396@...escale.com>,
	"Linus Walleij (linus.walleij@...aro.org)" <linus.walleij@...aro.org>,
	"Sascha Hauer (s.hauer@...gutronix.de)" <s.hauer@...gutronix.de>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"kernel@...gutronix.de" <kernel@...gutronix.de>,
	"cjb@...top.org" <cjb@...top.org>,
	Dong Aisheng <dongas86@...il.com>,
	"Shawn Guo (shawn.guo@...aro.org)" <shawn.guo@...aro.org>,
	Thomas Abraham <thomas.abraham@...aro.org>,
	"Grant Likely (grant.likely@...retlab.ca)" 
	<grant.likely@...retlab.ca>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: Pinmux bindings proposal V2

* Simon Glass <sjg@...omium.org> [120127 07:12]:
> 
> On Thu, Jan 26, 2012 at 6:21 PM, Tony Lindgren <tony@...mide.com> wrote:
> >
> > Maybe we need two bindings: A minimal subset of what Stephen is suggesting
> > that can handle 95% of the muxes with minimal overhead, then what you're
> > suggesting for the few muxes that need multiple states?
> 
> Perhaps that would work, it certainly deals nicely with making the
> rare cases less ugly if indeed they are rare. Of course a single
> binding that is not too ugly and still reasonably efficient would be
> best.
> 
> I will have a think about this a bit more and see if anything leaps
> out. It's quite an interesting problem...

Just to try to recap what has come up so far:

1. We need to avoid bloating things for basic cases to initialize
   several hundred pins.

2. Some muxes need to define multiple states.

3. We need to pass a flag for each mux to know whether or
   not it can be freed after init.

So how about let's do separate static and dynamic bindings,
something like this:

	/*
	 * Static init time only mux where
	 * we only specify phandle to driver
	 * and, offset of the mux, and the value.
	 * These pins are discarded after init.
	 *
	 * Format:	  mux_ctrl      offset value
	 */
	pinctrl-static = <&pmx_driver1  0x0020 0x1245
			   &pmx_driver2 0x0022 0x6578>;

	/*
	 * Dynamic mux where the mux is kept around after
	 * init and multiple states can be defined for
	 * a mux as a subnode of the pinmux controller.
	 *
	 * Format:	   mux_phandle   initial state
	 */ 
	pinctrl-dynamic = <&pmx_sdhci    PMX_STATE_ENABLED
			   &pmx_ehci_xcv PMX_STATE_ENABLED>;

This would make pinctrl-static binding follow the same
standard as GPIO binding and can be parsed easily with
of_parse_phandle_with_args.

Then for pinctrl-dynamic we can make a custom parser,
and the binding can follow the more readable format as
Simon posted.

Regards,

Tony
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