linux-kernel - Re: [PATCH v16 03/10] video: backlight: Add of_find

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Date:   Tue, 16 Jan 2018 17:56:49 +0100
From:   Noralf Trønnes <noralf@...nnes.org>
To:     Meghana Madhyastha <meghana.madhyastha@...il.com>,
        Lee Jones <lee.jones@...aro.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Sean Paul <seanpaul@...omium.org>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v16 03/10] video: backlight: Add of_find_backlight helper
 in backlight.c


Den 16.01.2018 11.33, skrev Meghana Madhyastha:
> Add of_find_backlight, a helper function which is a generic version
> of tinydrm_of_find_backlight that can be used by other drivers to avoid
> repetition of code and simplify things.
>
> Signed-off-by: Meghana Madhyastha <meghana.madhyastha@...il.com>
> ---
> Changes in v16:
> -Add comment about brightness in of_find_backlight
>
>   drivers/video/backlight/backlight.c | 40 +++++++++++++++++++++++++++++++++++++
>   include/linux/backlight.h           | 19 ++++++++++++++++++
>   2 files changed, 59 insertions(+)
>
> diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c
> index 8049e7656..7e4a5d77d 100644
> --- a/drivers/video/backlight/backlight.c
> +++ b/drivers/video/backlight/backlight.c
> @@ -580,6 +580,46 @@ struct backlight_device *of_find_backlight_by_node(struct device_node *node)
>   EXPORT_SYMBOL(of_find_backlight_by_node);
>   #endif
>   
> +/**
> +  * of_find_backlight - Get backlight device
> +  * @dev: Device
> +  *
> +  * This function looks for a property named 'backlight' on the DT node
> +  * connected to @dev and looks up the backlight device.
> +  *
> +  * Call backlight_put() to drop the reference on the backlight device.
> +  * gpio_backlight uses brightness as power state during probe.

I was thinking the gpio_backlight issue to be a comment with the code, 
not the docs.
Isn't this sentence a bit confusing as part of the docs?

checkpatch complains:
-:21: WARNING: Block comments should align the * on each line
-:72: WARNING: Block comments should align the * on each line

Noralf.

> +  *
> +  * Returns:
> +  * A pointer to the backlight device if found.
> +  * Error pointer -EPROBE_DEFER if the DT property is set, but no backlight
> +  * device is found.
> +  * NULL if there's no backlight property.
> +  */
> +struct backlight_device *of_find_backlight(struct device *dev)
> +{
> +	struct backlight_device *bd = NULL;
> +	struct device_node *np;
> +
> +	if (!dev)
> +		return NULL;
> +
> +	if (IS_ENABLED(CONFIG_OF) && dev->of_node) {
> +		np = of_parse_phandle(dev->of_node, "backlight", 0);
> +		if (np) {
> +			bd = of_find_backlight_by_node(np);
> +			of_node_put(np);
> +			if (!bd)
> +				return ERR_PTR(-EPROBE_DEFER);
> +			if (!bd->props.brightness)
> +				bd->props.brightness = bd->props.max_brightness;
> +		}
> +	}
> +
> +	return bd;
> +}
> +EXPORT_SYMBOL(of_find_backlight);
> +
>   static void __exit backlight_class_exit(void)
>   {
>   	class_destroy(backlight_class);
> diff --git a/include/linux/backlight.h b/include/linux/backlight.h
> index 7b6a9a2a3..32ea510da 100644
> --- a/include/linux/backlight.h
> +++ b/include/linux/backlight.h
> @@ -160,6 +160,16 @@ static inline int backlight_disable(struct backlight_device *bd)
>   	return backlight_update_status(bd);
>   }
>   
> +/**
> +  * backlight_put - Drop backlight reference
> +  * @bd: the backlight device to put
> +  */
> +static inline void backlight_put(struct backlight_device *bd)
> +{
> +	if (bd)
> +		put_device(&bd->dev);
> +}
> +
>   extern struct backlight_device *backlight_device_register(const char *name,
>   	struct device *dev, void *devdata, const struct backlight_ops *ops,
>   	const struct backlight_properties *props);
> @@ -203,4 +213,13 @@ of_find_backlight_by_node(struct device_node *node)
>   }
>   #endif
>   
> +#if IS_ENABLED(CONFIG_BACKLIGHT_CLASS_DEVICE)
> +struct backlight_device *of_find_backlight(struct device *dev);
> +#else
> +static inline struct backlight_device *of_find_backlight(struct device *dev)
> +{
> +	return NULL;
> +}
> +#endif
> +
>   #endif