linux-kernel - Re: Pinmux bindings proposal

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Date:	Wed, 18 Jan 2012 13:22:19 -0700
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Tony Lindgren <tony@...mide.com>
Cc:	Shawn Guo <shawn.guo@...aro.org>,
	"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

On Wed, Jan 18, 2012 at 08:29:43AM -0800, Tony Lindgren wrote:
> * 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.

Yes, the actual layout parsing should remain in the control of the
pinmux controller like it does for irqs, gpios, etc.

g.
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