linux-kernel - Re: [PATCH 2/4] pinmux: Add TB10x pinmux driver

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Date:	Thu, 18 Jul 2013 13:54:18 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Christian Ruppert <christian.ruppert@...lis.com>
CC:	Linus Walleij <linus.walleij@...aro.org>,
	Patrice CHOTARD <patrice.chotard@...com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	Rob Landley <rob@...dley.net>,
	Sascha Leuenberger <sascha.leuenberger@...lis.com>,
	Pierrick Hascoet <pierrick.hascoet@...lis.com>,
	devicetree-discuss@...ts.ozlabs.org, linux-doc@...r.kernel.org,
	Alexandre Courbot <acourbot@...dia.com>
Subject: Re: [PATCH 2/4] pinmux: Add TB10x pinmux driver

On 07/18/2013 10:07 AM, Christian Ruppert wrote:
...
> Well, perhaps my definition of "inside"/"outside" pins was not quite
> clear: The pin groups define the set of (kernel internal) pin numbers of
> "outside" pins which are used by pin controller to map a given
> interface. Inside pins are not numbered and the inside interfaces are
> only used to determine which outside pins are part of the same group
> (namely those for which the pin controller hardware provides a mux
> connection to the same inside interface):
> 
>                        4
>                 4  /|--/-- SPI
>    PINS[0..3] --/--||  4
>                    \|--/-- GPIO[0..3]
> 
>                    4
>    PINS[4..7] -----/------ GPIO[4..7]
> 
>                        2
>                 2  /|--/-- I2C
>    PINS[8..9] --/--||  2
>                    \|--/-- GPIO[8..9]
> 
> Pins 0..3 are in the SPI group because on the "inside" they can be muxed
> to the SPI interface.
> Pins 8..9 are in the I2C group because on the "inside" they can be muxed
> to the I2C interface.
> Pins 0..9 are in the GPIO group because on the "inside" they can be
> muxed to the GPIO controller.
> 
> All pin numbers are relative to the "outside", however, or conflict
> management would not be possible. I hope this is more understandable
> than my previous explanations.
> Both muxes are controlled by the same register. In our overly simplistic
> example this is not strictly necessary but in reality you might have pin
> conflicts between the different interfaces.

Same register, or same field/bits in that register?

If it's the same field/bits, I would expect to see the following pin groups:

1) PINS[0..3], PINS[8..9]
2) PINS[4..7]

... since those are the things that are independently muxable.
Otherwise, I'd expect to see the following groups:

1) PINS[0..3]
2) PINS[4..7]
3) PINS[8..9]

> After the discussion we had so far I'm not so sure if extending the
> pinctrl system with this kind of features is a very good idea.

That makes things simple:-)

One thing I still don't understand; in a previous mail, you'd mentioned
3 DT properties for configuring the pinmux; one represented the pin
group, one represented the mux function that was selected for that pin
group, and there was a third ("config"?) property. I still don't
understand that third property. I only see pins/pingroups and mux
functions in the diagram I quoted above.
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