linux-kernel - Re: [PATCH v2 1/2] led: led-class: Read max-brightness from devicetree

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Message-ID: <3e8e7834-fe0e-7e92-5472-cb9fd223980e@gmail.com>
Date:   Sat, 1 Jul 2023 13:09:28 +0200
From:   Jacek Anaszewski <jacek.anaszewski@...il.com>
To:     Astrid Rost <astrid.rost@...s.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Rob Herring <robh@...nel.org>, Pavel Machek <pavel@....cz>,
        Lee Jones <lee@...nel.org>
Cc:     kernel@...s.com, linux-leds@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] led: led-class: Read max-brightness from
 devicetree

Hi Astrid,

On 6/30/23 11:22, Astrid Rost wrote:
> Add max-brightness in order to reduce the current on the connected LEDs.
> Normally, the maximum brightness is determined by the hardware, and this
> property is not required. This property is used to set a software limit.
> It could happen that an LED is made so bright that it gets damaged or
> causes damage due to restrictions in a specific system, such as mounting
> conditions. Note that led-max-microamp should be preferably used, if it
> is supported by the controller.
> 
> Signed-off-by: Astrid Rost <astrid.rost@...s.com>
> ---
>   drivers/leds/led-class.c | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
> index 9255bc11f99d..ce652abf9336 100644
> --- a/drivers/leds/led-class.c
> +++ b/drivers/leds/led-class.c
> @@ -457,6 +457,10 @@ int led_classdev_register_ext(struct device *parent,
>   			if (fwnode_property_present(init_data->fwnode,
>   						    "retain-state-shutdown"))
>   				led_cdev->flags |= LED_RETAIN_AT_SHUTDOWN;
> +
> +			fwnode_property_read_u32(init_data->fwnode,
> +				"max-brightness",
> +				&led_cdev->max_brightness);
>   		}
>   	} else {
>   		proposed_name = led_cdev->name;

We have led-max-microamp for that and every LED class driver is supposed
to calculate its max brightness level basing on it.

-- 
Best regards,
Jacek Anaszewski