linux-kernel - Re: [RFC PATCH v3 2/5] pinctrl: add dt binding support for pinmux mappings

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Date:	Mon, 9 Jan 2012 09:56:27 +0800
From:	Shawn Guo <shawn.guo@...aro.org>
To:	Richard Zhao <richard.zhao@...aro.org>
Cc:	Stephen Warren <swarren@...dia.com>,
	"linus.walleij@...ricsson.com" <linus.walleij@...ricsson.com>,
	"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>,
	"Simon Glass (sjg@...omium.org)" <sjg@...omium.org>,
	"cjb@...top.org" <cjb@...top.org>,
	Dong Aisheng-B29396 <B29396@...escale.com>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Dong Aisheng <dongas86@...il.com>
Subject: Re: [RFC PATCH v3 2/5] pinctrl: add dt binding support for pinmux
 mappings

On Sun, Jan 08, 2012 at 08:51:59PM +0800, Richard Zhao wrote:
...
> > > So, this does appear to be conflating the two things: The definition of
> > > what pins are in a pingroup, and the mux function for a particular
> > > setting of that pingroup. I think you need separate nodes for this.
> > > 
> > At least for imx, we do not have mux function setting for pingroup.
> > Instead, it only applies to individual pin.
> I think it depends on function definition of pinmux driver. For the
> imx example patch, it's one-to-one.

It should depend on particular imx soc pinmux design rather than
pinmux driver.  If it's always one-to-one case, we do not need
pinmux at all.  Aisheng's patch just did not enumerate all the groups
for given function.  Instead, it puts a couple simple examples there
for demonstration.

...

> > > 		uart4func: func@1 {
> > > 			func-name = "uart4";
> > > 			locations = <&bargrp &bazgrp>;
> > > 			mux-value = <6 3>;
> > > 		};
> > 
> > I prefer to have function node defined in <board>.dtsi, since it's
> > all about defining phandle to the correct pingroup, which should be
> > decided by board design.
> group and function are one-to-one mapped for imx.

Again, it's not the case.

> So if you put function
> in board dts, why not put pin group there too?

If we put pingroup data in <board>.dts, the data will be likely get
duplicated a lot in different board dts files.  For example, if
imx6q-sabrelite chooses the same pingroup for usdhc3 and usdhc4 as
imx6q-arm2, the pingroup data will be duplicated between imx6q-arm2.dts
and imx6q-sabrelite.dts.

On the contrary, putting pingroup data in <soc>.dtsi and having function
node in <board>.dts with phandle pointing to the correct pingroup will
help avoid such data duplication.

-- 
Regards,
Shawn
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