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

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Date:	Wed, 10 Jul 2013 13:27:52 -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 07/08/2013 07:02 AM, Christian Ruppert wrote:
...
> OK, a small drawing of our hardware should make this clear, let's take
> an imaginary example of one port with 10 pins, one i2c interface, one
> spi interface and one GPIO bank:
> 
>               | mux N-1|
>               +........+
>               |        |  2
>               |        +--/-- i2c
>               |        |
>            10 |        |  4
>    Pins  --/--+ mux N  +--/-- spi
>               |        |
>               |        |  10
>               |        +--/-- GPIO
>               |        |
>               +........+
>               | mux N+1|
>
> This example shows the mux N inside the pin controller. It controls
> all pins associated to port N through a single register value M. Let's
> assume the pins are configured as follows in function of the register
> value:
> 
>  pin      M=0       M=1     M=2      M=3
>   0      GPIO0   SPI_MISO  GPIO0   SPI_MISO
>   1      GPIO1   SPI_MOSI  GPIO1   SPI_MOSI
>   2      GPIO2    SPI_CK   GPIO2    SPI_CK
>   3      GPIO3    SPI_CS   GPIO3    SPI_CS
>   4      GPIO4    GPIO4    GPIO4    GPIO4
>   5      GPIO5    GPIO5    GPIO5    GPIO5
>   6      GPIO6    GPIO6    GPIO6    GPIO6
>   7      GPIO7    GPIO7    GPIO7    GPIO7
>   8      GPIO8    GPIO8   I2C_SDA  I2C_SDA
>   9      GPIO9    GPIO9   I2C_SCL  I2C_SCL


In that scenario, in the language of Linux's pinctrl subsystem, what you
have is:

10 pins, named 0..9
1 pin group, named perhaps "mux N".
4 different functions; values M==0, 1, 2, 3.

> We now have three pin groups defined, corresponding to the chip-side
> ports of the pin controller:
> GPIO = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
> SPI  = {0, 1, 2, 3}
> I2C  = {8, 9}

You would usually only define pin groups for the pin/ball/package side
of the pinmux HW. IIRC, you're also wanting to define pin groups for the
intra-chip side of the pinmux HW. However, you're not muxing functions
onto those pingroups; they're just there to help with naming the
GPIO<->pinmux mapping. You only mux functions onto the pin/ball/package
side pins/pingroups.


> abilis,pingrp now specifies one of the three pin groups. Note that I2C
>        and SPI can be requested independently in a completely orthogonal
>        manner: The information if I2C is reqired or not is confined to
>        the I2C request and does not leak into the SPI request as would
>        be the case if we configured the entire port at the same time.

The pingrp should represent the pin/ball/package side pins/groups. In
this case, it should specify "N".

> abilis,ioport specifies N.

That is replaced be pingrp.

> abilis,ioconf specifies M.

That'd be better named "function" or something like that, in order to
indicate that it specifies which function is mux'd onto the specified
pin(s)/pingroup(s).
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