linux-kernel - Re: Pinmux bindings proposal

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Message-ID: <20120118162943.GC22818@atomide.com>
Date:	Wed, 18 Jan 2012 08:29:43 -0800
From:	Tony Lindgren <tony@...mide.com>
To:	Shawn Guo <shawn.guo@...aro.org>
Cc:	Grant Likely <grant.likely@...retlab.ca>,
	"linus.walleij@...ricsson.com" <linus.walleij@...ricsson.com>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"kernel@...gutronix.de" <kernel@...gutronix.de>,
	"cjb@...top.org" <cjb@...top.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Dong Aisheng <dongas86@...il.com>
Subject: Re: Pinmux bindings proposal

* Tony Lindgren <tony@...mide.com> [120118 07:00]:
> * Shawn Guo <shawn.guo@...aro.org> [120118 05:57]:
> > On 18 January 2012 22:13, Tony Lindgren <tony@...mide.com> wrote:
> > > Hi,
> > >
> > > * Grant Likely <grant.likely@...retlab.ca> [120116 09:55]:
> > >> On Fri, Jan 13, 2012 at 12:39:42PM -0800, Stephen Warren wrote:
> > >> >                 pinmux =
> > >> >                         <"default" &pmx_sdhci_active>
> > >> >                         <"suspend" &pmx_sdhci_suspend>;
> > >> >
> > >> >                 /* 1:n example: */
> > >> >                 pinmux =
> > >> >                         <"default" &pmx_sdhci_mux_a>
> > >> >                         <"default" &pmx_sdhci_pincfg_a>
> > >> >                         <"suspend" &pmx_sdhci_mux_a>
> > >> >                         <"suspend" &pmx_sdhci_pincfg_a_suspend>;
> > >>
> > >>
> > >> Yeah, don't do this.  Mixing phandle, string and cell values in a
> > >> property gets messy and could become troublesome to parse.  I've
> > >> backed away from it in the clk binding.
> > >
> > > Yup, that's because the string is embedded directly into the mixed
> > > mode array and will likely make the following data unaligned. That
> > > means it's extremely flakey to parse, and will lead into horrible
> > > errors if you have typos in the .dts file.. Tried that and gave up
> > > on it.
> > >
> > > I think I've found a way to avoid using names at all, assuming we set
> > > each pin as a phandle for the drivers to use :)
> > >
> > The problem with doing that is we will have to represent each pin as a
> > node in device tree.  For imx6q case, we have 197 pins.  Doing so will
> > bloat the device tree.
> 
> Sure there's some overhead. I've got it working with 220 pins, it's
> not too bad as threre's not much string parsing involved.
> 
> I don't have all the devices mapping the pins though. The .dtb for
> omap4 is about 25k now.
> 
> If we wanted to avoid adding phandles for each pin, then we could do:
> 
> serial@...8020000 {
> 	compatible = "ti,8250";
> 	reg = <0x48020000 0x100>;
> 	reg-shift = <2>;
> 	interrupts = <106>;
> 
> 	/* controller, offset, value */
> 	pins = <&mux1 0xabcd 0x10
>                 &mux1 0xabcf 0x0>;
> };
> 
> But then the .dts file becomes an unreadable matrix unless we have
> a preprocessor..

Forgot to mention that as long as we all standardize to use something
common for #pin-args and of_parse_phandle_with_args(), the pin mapping
could depend on the pinmux driver for selecting whether or not to use
a phandle for each pin.

Tony
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