linux-kernel - Re: [RFC PATCH] leds: pwm: add flag to start without PWM init

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Message-ID: <68c56b10-7ebb-2bb4-213f-400e3f99ac40@gmail.com>
Date:   Mon, 9 Mar 2020 20:42:35 +0100
From:   Jacek Anaszewski <jacek.anaszewski@...il.com>
To:     Denis Osterland-Heim <denis.osterland@...hl.com>,
        "dmurphy@...com" <dmurphy@...com>, "pavel@....cz" <pavel@....cz>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-leds@...r.kernel.org" <linux-leds@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [RFC PATCH] leds: pwm: add flag to start without PWM init

Hi Denis,

There is already a property for that purpose: default-state = "keep";

Please just use it instead.

Best regards,
Jacek Anaszewski

On 3/9/20 9:24 AM, Denis Osterland-Heim wrote:
> This patch add "pwm,uninitalized" devicetree flag support to pwm
> leds, which allows to defer pwm init to first use of led.
> 
> This allows to configure the PWM early in bootloader to let the LED
> blink until an application in Linux userspace set something different.
> 
> Signed-off-by: Denis Osterland-Heim <Denis.Osterland@...hl.com>
> ---
> Hi,
> 
> I want to ask if such a patch is intresting for mainline and
> if it is woth to think about how to represent this state to user space.
> 
> Regards Denis
> 
>  Documentation/devicetree/bindings/leds/leds-pwm.txt |  1 +
>  drivers/leds/leds-pwm.c                             | 10 ++++++++--
>  include/linux/leds_pwm.h                            |  1 +
>  3 files changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/leds/leds-pwm.txt b/Documentation/devicetree/bindings/leds/leds-pwm.txt
> index 6c6583c35f2f..4f58df631fc9 100644
> --- a/Documentation/devicetree/bindings/leds/leds-pwm.txt
> +++ b/Documentation/devicetree/bindings/leds/leds-pwm.txt
> @@ -19,6 +19,7 @@ LED sub-node properties:
>    see Documentation/devicetree/bindings/leds/common.txt
>  - linux,default-trigger :  (optional)
>    see Documentation/devicetree/bindings/leds/common.txt
> +- pwm,uninitalized : defer PWM init to first brightness change of led
>  
>  Example:
>  
> diff --git a/drivers/leds/leds-pwm.c b/drivers/leds/leds-pwm.c
> index 8b6965a563e9..02c90f05602a 100644
> --- a/drivers/leds/leds-pwm.c
> +++ b/drivers/leds/leds-pwm.c
> @@ -97,7 +97,8 @@ static int led_pwm_add(struct device *dev, struct led_pwm_priv *priv,
>  	 * FIXME: pwm_apply_args() should be removed when switching to the
>  	 * atomic PWM API.
>  	 */
> -	pwm_apply_args(led_data->pwm);
> +	if (!led->pwm_uninitialized)
> +		pwm_apply_args(led_data->pwm);
>  
>  	pwm_get_args(led_data->pwm, &pargs);
>  
> @@ -108,7 +109,9 @@ static int led_pwm_add(struct device *dev, struct led_pwm_priv *priv,
>  	ret = devm_led_classdev_register(dev, &led_data->cdev);
>  	if (ret == 0) {
>  		priv->num_leds++;
> -		led_pwm_set(&led_data->cdev, led_data->cdev.brightness);
> +		if (!led->pwm_uninitialized)
> +			led_pwm_set(&led_data->cdev,
> +					led_data->cdev.brightness);
>  	} else {
>  		dev_err(dev, "failed to register PWM led for %s: %d\n",
>  			led->name, ret);
> @@ -143,6 +146,9 @@ static int led_pwm_create_fwnode(struct device *dev, struct led_pwm_priv *priv)
>  		fwnode_property_read_u32(fwnode, "max-brightness",
>  					 &led.max_brightness);
>  
> +		led.pwm_uninitialized = fwnode_property_read_bool(fwnode,
> +							"pwm,uninitialized");
> +
>  		ret = led_pwm_add(dev, priv, &led, fwnode);
>  		if (ret) {
>  			fwnode_handle_put(fwnode);
> diff --git a/include/linux/leds_pwm.h b/include/linux/leds_pwm.h
> index 93d101d28943..0b04dfd43654 100644
> --- a/include/linux/leds_pwm.h
> +++ b/include/linux/leds_pwm.h
> @@ -10,6 +10,7 @@ struct led_pwm {
>  	const char	*default_trigger;
>  	unsigned	pwm_id __deprecated;
>  	u8 		active_low;
> +	u8		pwm_uninitialized;
>  	unsigned 	max_brightness;
>  	unsigned	pwm_period_ns;
>  };
>