Re: [RFC] GPIO lines [was: GPIO User I/O]

[Rodolfo Giometti <giometti@xxxxxxxxxxxx>]

On 11/07/2020 17:21, Linus Walleij wrote:
> On Thu, Jul 9, 2020 at 4:11 PM Rodolfo Giometti <giometti@xxxxxxxxxxxx> wrote:
> 
>>         gpio_lines {
>>                 compatible = "gpio-line";
>>
>>                 bypass0 {
>>                         gpios = <&gpionb 10 GPIO_ACTIVE_HIGH>;
>>                         mode = "out-low";
>>                 };
>>
>>                 bypass1 {
>>                         gpios = <&gpiosb 11 GPIO_ACTIVE_HIGH>;
>>                         mode = "out-low";
>>                 };
>>
>>                 key {
>>                         gpios = <&gpionb 4 GPIO_ACTIVE_HIGH>;
>>                         mode = "input";
>>                 };
>>
>>                 motor {
>>                         gpios = <&gpionb 8 GPIO_ACTIVE_HIGH>;
>>                         mode = "out-high-open-drain";
>>                 };
> 
> These mode = ... strings are really just a big confusion for me since
> they reinvent several of the flags you can already give to the gpios,
> see include/dt-bindings/gpio/gpio.h:
> 
> /* Bit 0 express polarity */
> #define GPIO_ACTIVE_HIGH 0
> #define GPIO_ACTIVE_LOW 1
> 
> /* Bit 1 express single-endedness */
> #define GPIO_PUSH_PULL 0
> #define GPIO_SINGLE_ENDED 2
> 
> /* Bit 2 express Open drain or open source */
> #define GPIO_LINE_OPEN_SOURCE 0
> #define GPIO_LINE_OPEN_DRAIN 4
> 
> /*
>  * Open Drain/Collector is the combination of single-ended open drain interface.
>  * Open Source/Emitter is the combination of single-ended open source interface.
>  */
> #define GPIO_OPEN_DRAIN (GPIO_SINGLE_ENDED | GPIO_LINE_OPEN_DRAIN)
> #define GPIO_OPEN_SOURCE (GPIO_SINGLE_ENDED | GPIO_LINE_OPEN_SOURCE)

These modes came from include/linux/gpio/consumer.h:

/**
 * Optional flags that can be passed to one of gpiod_* to configure direction
 * and output value. These values cannot be OR'd.
 */
enum gpiod_flags {
        GPIOD_ASIS      = 0,
        GPIOD_IN        = GPIOD_FLAGS_BIT_DIR_SET,
        GPIOD_OUT_LOW   = GPIOD_FLAGS_BIT_DIR_SET | GPIOD_FLAGS_BIT_DIR_OUT,
        GPIOD_OUT_HIGH  = GPIOD_FLAGS_BIT_DIR_SET | GPIOD_FLAGS_BIT_DIR_OUT |
                          GPIOD_FLAGS_BIT_DIR_VAL,
        GPIOD_OUT_LOW_OPEN_DRAIN = GPIOD_OUT_LOW | GPIOD_FLAGS_BIT_OPEN_DRAIN,
        GPIOD_OUT_HIGH_OPEN_DRAIN = GPIOD_OUT_HIGH | GPIOD_FLAGS_BIT_OPEN_DRAIN,
};

So a setting like the following should set at boot gpio10 as output to 0:

bypass0 {
        gpios = <&gpionb 10 GPIO_ACTIVE_HIGH>;
        mode = "out-low";
};

While the next one should set gpio10 as output to 1:

bypass0 {
        gpios = <&gpionb 10 GPIO_ACTIVE_LOW>;
        mode = "out-low";
};

Maybe I can do something similar to hog-gpio as below, if you prefer...

bypass0 {
        gpios = <&gpionb 10 GPIO_ACTIVE_LOW>;
	output-low;
};

Ciao,

Rodolfo

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