[RFC 2/2] ARM:Tegra: Device Tree Support: Initialize audio card gpio's from the device tree.

[Grant Likely]

On Mon, May 30, 2011 at 1:20 PM, Grant Likely <grant.likely at secretlab.ca> wrote:
> On Mon, May 30, 2011 at 12:54 PM, Segher Boessenkool
> <segher at kernel.crashing.org> wrote:
>>>> I'm currently dealing with an SoC that has over a hundred GPIOs.
>>>> Whatever we choose, I think it should be able to handle an insane
>>>> number of GPIOs without getting any more cumbersome that is
>>>> necessary.
>>>
>>> This is *consumer* side GPIOs, not bindings for the device providing the
>>> GPIOs.  If a single device needs to use hundreds of GPIOs I'd expect
>>> many of them will be block functions so you'd have a binding with an
>>> array for things like "databus" and "addrbus".
>>
>> But please name them like "databus-gpio", so that it is obvious what it
>> is.  Also have to think about how this will work with multiple GPIO
>> controllers: do you require the GPIO controller node to be part of every
>> GPIO description, or do you do some "gpio-parent" scheme as well, how
>> does that interact with not having a single array of GPIOs?
>>
>> Better write this down as a binding, before committing to it :-)
>
> Here's my thinking: Exactly the same binding for "gpios" as is now,
> except can use different property names, like "chipsel-gpios" or
> "wp-gpio".  Here is a draft patch to the binding:

I know there is still some debate on this, but I'm going to go ahead
and commit this extension since it draws naturally from what we're
already using, and it does not preclude doing a node binding at some
point in the future.

g.

>
> diff --git a/Documentation/devicetree/bindings/gpio/gpio.txt
> b/Documentation/devicetree/bindings/gpio/gpio.txt
> index edaa84d..21dd4f9 100644
> --- a/Documentation/devicetree/bindings/gpio/gpio.txt
> +++ b/Documentation/devicetree/bindings/gpio/gpio.txt
> @@ -4,17 +4,45 @@ Specifying GPIO information for devices
>  1) gpios property
>  -----------------
>
> -Nodes that makes use of GPIOs should define them using `gpios' property,
> -format of which is: <&gpio-controller1-phandle gpio1-specifier
> -                    &gpio-controller2-phandle gpio2-specifier
> -                    0 /* holes are permitted, means no GPIO 3 */
> -                    &gpio-controller4-phandle gpio4-specifier
> -                    ...>;
> +Nodes that makes use of GPIOs should specify them using one or more
> +properties, each containing a 'gpio-list':
>
> -Note that gpio-specifier length is controller dependent.
> +       gpio-list ::= <single-gpio> [gpio-list]
> +       single-gpio ::= <gpio-phandle> <gpio-specifier>
> +       gpio-phandle : phandle to gpio controller node
> +       gpio-specifier : Array of #gpio-cells specifying specific gpio
> +                        (controller specific)
> +
> +GPIO properties should be named either "gpios" or "*-gpio".  Exact
> +meaning of each gpio property must be documented in the device tree
> +binding for each device.
> +
> +For example, the following could be used to describe gpios pins to use
> +as chip select lines; with chip selects 0, 1 and 3 populated, and chip
> +select 2 left empty:
> +
> +       gpio1: gpio1 {
> +               gpio-controller
> +                #gpio-cells = <2>;
> +       };
> +       gpio2: gpio2 {
> +               gpio-controller
> +                #gpio-cells = <1>;
> +       };
> +       [...]
> +        chipsel-gpio = <&gpio1 12 0>,
> +                       <&gpio1 13 0>,
> +                       <0>, /* holes are permitted, means no GPIO 2 */
> +                       <&gpio2 2>;
> +
> +Note that gpio-specifier length is controller dependent.  In the
> +above example, &gpio1 uses 2 cells to specify a gpio, while &gpio2
> +only uses one.
>
>  gpio-specifier may encode: bank, pin position inside the bank,
>  whether pin is open-drain and whether pin is logically inverted.
> +Exact meaning of each specifier cell is controller specific, and must
> +be documented in the device tree binding for the device.
>
>  Example of the node using GPIOs:
>
> @@ -28,8 +56,8 @@ and empty GPIO flags as accepted by the "qe_pio_e"
> gpio-controller.
>  2) gpio-controller nodes
>  ------------------------
>
> -Every GPIO controller node must have #gpio-cells property defined,
> -this information will be used to translate gpio-specifiers.
> +Every GPIO controller node must both an empty "gpio-controller"
> +property, and have #gpio-cells contain the size of the gpio-specifier.
>
>  Example of two SOC GPIO banks defined as gpio-controller nodes:
>



-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.