linux-kernel - Re: [PATCH] leds: leds-gpio: Add a condition check for active low leds.

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Date:   Wed, 5 Sep 2018 09:44:04 +0200
From:   Michal Vokáč <michal.vokac@...ft.com>
To:     Song Qiang <songqiang1304521@...il.com>, jacek.anaszewski@...il.com
Cc:     pavel@....cz, robh+dt@...nel.org, mark.rutland@....com,
        linux-leds@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Song Qiang <songqiang.1304521@...il.com>
Subject: Re: [PATCH] leds: leds-gpio: Add a condition check for active low
 leds.

Hi Song,
On 5.9.2018 04:34, Song Qiang wrote:
> Some leds on our board are active low leds, which means these leds
> are lighted when the corresponding gpio line is low, while the
> original leds-gpio driver default all leds are active high leds.
> This patch adds a devicetree node "light-state", whose value should
> be "high" for active high leds and "low" for active low leds.
> The default value is "high" for compatible for the original driver.
> 
> Signed-off-by: Song Qiang <songqiang.1304521@...il.com>
> ---
>   .../devicetree/bindings/leds/leds-gpio.txt    | 15 +++++++++++
>   drivers/leds/leds-gpio.c                      | 25 +++++++++++++++++--
>   2 files changed, 38 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/leds/leds-gpio.txt b/Documentation/devicetree/bindings/leds/leds-gpio.txt
> index a48dda268f81..0a8fad75c704 100644
> --- a/Documentation/devicetree/bindings/leds/leds-gpio.txt
> +++ b/Documentation/devicetree/bindings/leds/leds-gpio.txt
> @@ -23,6 +23,9 @@ LED sub-node properties:
>     remains up.
>   - panic-indicator : (optional)
>     see Documentation/devicetree/bindings/leds/common.txt
> +- light-state: (optional) Values should be "high" or "low", which indicates
> +	the state of the GPIO pin when the led is on.
> +  see Documentation/devicetree/bindings/leds/common.txt
>   
>   Examples:
>   
> @@ -64,3 +67,15 @@ leds {
>   		retain-state-suspended;
>   	};
>   };
> +
> +leds {
> +	compatible = "gpio-leds";
> +
> +	led0 {
> +		label = "led0";
> +		gpios = <&gpio1 19 GPIO_ACTIVE_HIGH>;

With this patch you are introducing one more way to invert the logic.
If your LED is active LOW, you should use GPIO_ACTIVE_LOW in your DT.
All should work as expected then.

Best regards,
Michal

> +		linux,default-trigger = "heartbeat";
> +		default-state = "off";
> +		light-state = "low";
> +	};
> +}
> diff --git a/drivers/leds/leds-gpio.c b/drivers/leds/leds-gpio.c
> index 764c31301f90..463ded0c71ac 100644
> --- a/drivers/leds/leds-gpio.c
> +++ b/drivers/leds/leds-gpio.c
> @@ -26,9 +26,13 @@ struct gpio_led_data {
>   	struct gpio_desc *gpiod;
>   	u8 can_sleep;
>   	u8 blinking;
> +	u8 light_state;
>   	gpio_blink_set_t platform_gpio_blink_set;
>   };
>   
> +#define LEDS_GPIO_LIGHTSTATE_HIGH	0
> +#define LEDS_GPIO_LIGHTSTATE_LOW	1
> +
>   static inline struct gpio_led_data *
>   			cdev_to_gpio_led_data(struct led_classdev *led_cdev)
>   {
> @@ -42,9 +46,15 @@ static void gpio_led_set(struct led_classdev *led_cdev,
>   	int level;
>   
>   	if (value == LED_OFF)
> -		level = 0;
> +		if (led_dat->light_state == LEDS_GPIO_LIGHTSTATE_HIGH)
> +			level = 0;
> +		else
> +			level = 1;
>   	else
> -		level = 1;
> +		if (led_dat->light_state == LEDS_GPIO_LIGHTSTATE_HIGH)
> +			level = 1;
> +		else
> +			level = 0;
>   
>   	if (led_dat->blinking) {
>   		led_dat->platform_gpio_blink_set(led_dat->gpiod, level,
> @@ -205,6 +215,17 @@ static struct gpio_leds_priv *gpio_leds_create(struct platform_device *pdev)
>   				led.default_state = LEDS_GPIO_DEFSTATE_OFF;
>   		}
>   
> +		if (!fwnode_property_read_string(child, "light-state",
> +						 &state)) {
> +			if (!strcmp(state, "low"))
> +				led_dat->light_state =
> +					LEDS_GPIO_LIGHTSTATE_LOW;
> +			else{
> +				led_dat->light_state =
> +					LEDS_GPIO_LIGHTSTATE_HIGH;
> +			}
> +		}
> +
>   		if (fwnode_property_present(child, "retain-state-suspended"))
>   			led.retain_state_suspended = 1;
>   		if (fwnode_property_present(child, "retain-state-shutdown"))
>