On Fri, Jan 9, 2015 at 7:26 PM, Ray Jui [off-list ref] wrote:

On 1/9/2015 2:12 AM, Linus Walleij wrote:

quoted

Just use "groups" and "function" and refer to
Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt

Then "alt1", "alt2" etc are non-functional names of functions.
Use the real function names, like "spi0" or so. This
alt-business seems to be just a shortcut to make it
simple, don't do that.

Then you use e.g. "spi0" as a group name. I prefer you
call that "spi0_grp" or something to say it is a group of
pins associated with spi0, as spi0 is actually the
function.

Hmmm, I did this by following brcm,bcm11351-pinctrl.txt:
- function: String. Specifies the pin mux selection. Values must be one
of: "alt1", "alt2", "alt3", "alt4"

But you are right, in the pinctrl binding document it describes the
generic pin multiplexing nodes use "function" and "group".

Note "function" and "groups". Note groups is pluralis. You can
select multiple groups for a single function.

For example, the group "lcd" covers 30 pins. When I configure "lcd" to
alternate function 1, all 30 pins are muxed to LCD function. When
configured to function 2, all pins are muxed to SRAM function. Now, here
comes the issue, when configured to function 3, pins 1-15 and 20-30
become GPIO function, but pins 16-19 becomes SPI5 function. When it's
configured to function 4, all 30 pins become GPIO.

I would split the use case in two groups for LCD and SRAM,
and three groups for GPIO:
"lcd_grp", "sram_grp", "gpio-1-15_grp",
"gpio-16-19_grp", "gpio-20-30_grp", "spi5_grp"

Valid combinations become

function = "lcd"
groups = "lcd_grp";

function = "sram"
groups = "sram_grp"

For all GPIO only this:

function = "gpio"
groups = "gpio-1-16_grp", "gpio-16-19_grp", "gpio-20-30_grp"

For a combined GPIO+SPI:

function = "gpio"
groups = "gpio-1-16_grp", "gpio-20-30_grp"

function = "spi5"
groups = "spi5_grp"

The pinctrl runtile will protest if you try to combine spi5_grp
with gpio-16-19_grp.

In some other cases, when I configure a group to other functions, there
could be spare pins which become unused (not brought out to the pad).
Or, the spare pins may also become a separate function.

That's cool.

Based on the LCD example, I'd assume I would do the following for the
default LCD function:

lcd_node {
        group = "lcd_grp";
        function = "lcd";
};

And in the case of function 3, I would call the function "spi5" and
assume the rest of pins become either GPIO (or unused)?

spi5_node {
        group = "lcd_grp";
        function = "spi5";
};

Looks cool per above.

You need some clever code in the driver to handle double-configuration
of registers and so on, but I think it can be done.

Using pin control as a GPIO backend can be a bit tricky and will need
some testing and elaboration, but the subsystem will block collisions.

Yours,
Linus Walleij