Re: Query on using leds-gpio driver on a. GPIO with ACTIVE_HIGH

[Jacek Anaszewski <jacek.anaszewski@gmail.com>]

Hi Vishwanatha,

On 7/6/20 9:19 AM, Vishwanatha Subbanna wrote:
> Hello,
> 
> I have been a user of “leds-gpio” driver to manage the LEDs on IBM servers. So far, all these LEDs that were controlled by GPIO were ACTIVE_LOW.
> 
> Example from DTS.
> 
>          fan3 {
>              retain-state-shutdown;
>              default-state = "keep";
>              gpios = <&pca0 3 GPIO_ACTIVE_LOW>;
>          };
> 
> I wanted to know if it makes any difference to the user if the GPIO is ACTIVE_HIGH. I read through https://www.kernel.org/doc/Documentation/gpio/board.txt and it seemed we should be able to use it.
> 
> However, going through https://github.com/torvalds/linux/blob/master/drivers/leds/leds-pca955x.c, I am not quite sure if the ACTIVE_HIGH can be used same as ACTIVE_LOW since I saw these :
> 
> 
> #define PCA955X_LS_LED_ON	0x0	/* Output LOW */
> #define PCA955X_LS_LED_OFF	0x1	/* Output HI-Z */
> 
> #define PCA955X_GPO_HIGH	LED_OFF
> #define PCA955X_GPIO_LOW	LED_FULL
> 
> 
> This will be my DT entry :
> 
>          fan3 {
>              retain-state-shutdown;
>              default-state = "keep";
>              gpios = <&pca0 3 GPIO_ACTIVE_HIGH>;
>          };
> 
> Will I be able to use the same “leds-gpio” interfaces irrespective of GPIO_LOW / GPIO_HIGH ?
> 
> I use these interfaces today:
> 
> echo 255 > brightness —> Turn Solid_ON
> echo 0 > brightness —> Turn OFF
> echo “timer” > trigger —> Initiate Blink
> echo “none” > trigger —> Terminate Blink

 From what I can see in gpiolib sources GPIO_ACTIVE_LOW results
in reversing the logic, i.e. pca955x_gpio_set_value() will
be passed 0 when setting gpio to 1.

Experience doesn't corroborate that?

-- 
Best regards,
Jacek Anaszewski