linux-kernel - Re: [PATCH v2] backlight: led

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Message-ID: <20230705140943.GC6265@aspen.lan>
Date:   Wed, 5 Jul 2023 15:09:43 +0100
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Mans Rullgard <mans@...sr.com>
Cc:     Lee Jones <lee@...nel.org>, Jingoo Han <jingoohan1@...il.com>,
        Helge Deller <deller@....de>, dri-devel@...ts.freedesktop.org,
        linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] backlight: led_bl: fix initial power state

On Tue, Jul 04, 2023 at 05:19:52PM +0100, Mans Rullgard wrote:
> The condition for the initial power state based on the default
> brightness value is reversed.  Fix it.
>
> Furthermore, use the actual state of the LEDs rather than the default
> brightness specified in the devicetree as the latter should not cause
> the backlight to be automatically turned on.
>
> If the backlight device is not linked to any display, set the initial
> power to on unconditionally.
>
> Fixes: ae232e45acf9 ("backlight: add led-backlight driver")
> Signed-off-by: Mans Rullgard <mans@...sr.com>
> ---
> Changes in v2:
> - Use the reported LED state to set initial power state
> - Always power on if no phandle in DT
> ---
>  drivers/video/backlight/led_bl.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/video/backlight/led_bl.c b/drivers/video/backlight/led_bl.c
> index 3259292fda76..bbf1673b1fb0 100644
> --- a/drivers/video/backlight/led_bl.c
> +++ b/drivers/video/backlight/led_bl.c
> @@ -176,6 +176,7 @@ static int led_bl_probe(struct platform_device *pdev)
>  {
>  	struct backlight_properties props;
>  	struct led_bl_data *priv;
> +	int init_brightness;
>  	int ret, i;
>
>  	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
> @@ -190,6 +191,8 @@ static int led_bl_probe(struct platform_device *pdev)
>  	if (ret)
>  		return ret;
>
> +	init_brightness = priv->default_brightness;
> +
>  	ret = led_bl_parse_levels(&pdev->dev, priv);
>  	if (ret < 0) {
>  		dev_err(&pdev->dev, "Failed to parse DT data\n");
> @@ -200,8 +203,8 @@ static int led_bl_probe(struct platform_device *pdev)
>  	props.type = BACKLIGHT_RAW;
>  	props.max_brightness = priv->max_brightness;
>  	props.brightness = priv->default_brightness;
> -	props.power = (priv->default_brightness > 0) ? FB_BLANK_POWERDOWN :
> -		      FB_BLANK_UNBLANK;
> +	props.power = (init_brightness || !pdev->dev.of_node->phandle) ?
> +		FB_BLANK_UNBLANK : FB_BLANK_POWERDOWN;

I was rather expecting to see a comment in the code here... it's super
hard to figure out the purpose of the phandle check otherwise.


Daniel.