Pinmux bindings proposal

[Grant Likely]

On Wed, Jan 18, 2012 at 07:32:56AM -0800, Tony Lindgren wrote:
> * Shawn Guo <shawn.guo at linaro.org> [120118 05:57]:
> > On 18 January 2012 22:13, Tony Lindgren <tony at atomide.com> wrote:
> > > Hi,
> > >
> > > * Grant Likely <grant.likely at secretlab.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 at 0x48020000 {
> 	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..

One node per pin does get excessive in a hurry.  I prefer the one node
per pin controller.  Tools can be written to make writing the
definition easier.

g.