linux-kernel - Re: Pinmux bindings proposal

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Date:	Wed, 18 Jan 2012 22:30:28 +0800
From:	Shawn Guo <shawn.guo@...aro.org>
To:	Tony Lindgren <tony@...mide.com>
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

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.

-- 
Regards,
Shawn
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