Re: [PATCH v3 10/13] backlight: add overview and update existing doc

[Daniel Thompson <daniel.thompson@linaro.org>]

On Mon, Jun 01, 2020 at 08:52:04AM +0200, Sam Ravnborg wrote:
> Add overview chapter to backlight.c.
> Update existing kernel-doc to follow a more consistent
> style and drop kernel-doc for deprecated functions.
> 
> v2:
>   - Sevaral editorial corrections that makes reading
>     much easier (Daniel)
>   - Spelling fixes (Daniel)
>   - updated intro chapter with a little more info
> 
> Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

Two very small nits... but one will affect formatted output so I had to
raise it. Feel free add my Reviewed-by: when recirculating!


Daniel.


> Cc: Lee Jones <lee.jones@linaro.org>
> Cc: Daniel Thompson <daniel.thompson@linaro.org>
> Cc: Jingoo Han <jingoohan1@gmail.com>
> ---
>  drivers/video/backlight/backlight.c | 131 +++++++++++++++++++---------
>  1 file changed, 90 insertions(+), 41 deletions(-)
> 
> diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c
> index 17f04cff50ab..06bcddd76a7e 100644
> --- a/drivers/video/backlight/backlight.c
> +++ b/drivers/video/backlight/backlight.c
> @@ -22,6 +22,46 @@
>  #include <asm/backlight.h>
>  #endif
>  
> +/**
> + * DOC: overview
> + *
> + * The backlight core supports implementing backlight drivers.
> + *
> + * A backlight driver registers a driver using
> + * devm_backlight_device_register(). The properties of the backlight
> + * driver such as type and max_brightness must be specified.
> + * When the core detect changes in for example brightness or power state
> + * the update_status() operation is called. The backlight driver shall
> + * implement this operation and use it to adjust backlight.
> + *
> + * Several sysfs attributes are provided by the backlight core::
> + *
> + * - brightness         R/W, set the requested brightness level
> + * - actual_brighness   RO, the brightness level used by the HW
> + * - max_brightness     RO, the maximum  brightness level supported
> + *
> + * See Documentation/ABI/stable/sysfs-class-backlight for the full list.
> + *
> + * The backlight can be adjusted using the sysfs interface, and
> + * the backlight driver may also support adjusting backlight using
> + * a hot-key or some other platfrom or firmware specific way.
> + *
> + * The driver shall implement the get_brightness() operation if

I overlooked this before but this reads better with "must" rather
than "shall". It's not wrong to use shall but I think it is more
idiomatic to use "must".


> + * the HW do not support all the levels that can be specified in
> + * brightness, thus providing user-space access to the actual level
> + * via the actual_brightness attribute.
> + * When the backlight changes this is reported to user-space using

Missing newline between paragraphs...


> + * an uevent connected to the actual_brightness attribute.
> + * When brightness is set by platform specific means, for example
> + * a hot-key to adjust backlight, the driver must notify the backlight
> + * core that brightness has changed using backlight_force_update().
> + *
> + * The backlight driver core receives notifications from fbdev and
> + * if the event is FB_EVENT_BLANK and if the value of blank, from the
> + * FBIOBLANK ioclt, results in a change in the backlight state the
> + * update_status() operation is called.
> + */
> +
>  static struct list_head backlight_dev_list;
>  static struct mutex backlight_dev_list_mutex;
>  static struct blocking_notifier_head backlight_notifier;
> @@ -40,9 +80,17 @@ static const char *const backlight_scale_types[] = {
>  
>  #if defined(CONFIG_FB) || (defined(CONFIG_FB_MODULE) && \
>  			   defined(CONFIG_BACKLIGHT_CLASS_DEVICE_MODULE))
> -/* This callback gets called when something important happens inside a
> - * framebuffer driver. We're looking if that important event is blanking,
> - * and if it is and necessary, we're switching backlight power as well ...
> +/*
> + * fb_notifier_callback
> + *
> + * This callback gets called when something important happens inside a
> + * framebuffer driver. The backlight core only cares about FB_BLANK_UNBLANK
> + * which is reported to the driver using backlight_update_status()
> + * as a state change.
> + *
> + * There may be several fbdev's connected to the backlight device,
> + * in which case they are kept track of. A state change is only reported
> + * if there is a change in backlight for the specified fbdev.
>   */
>  static int fb_notifier_callback(struct notifier_block *self,
>  				unsigned long event, void *data)
> @@ -318,12 +366,15 @@ static struct attribute *bl_device_attrs[] = {
>  ATTRIBUTE_GROUPS(bl_device);
>  
>  /**
> - * backlight_force_update - tell the backlight subsystem that hardware state
> - *   has changed
> + * backlight_force_update - force an update due to a hardware change
>   * @bd: the backlight device to update
> + * @reason: the method used for the backlight update
>   *
>   * Updates the internal state of the backlight in response to a hardware event,
> - * and generate a uevent to notify userspace
> + * and generates an uevent to notify userspace. A backlight driver shall call
> + * backlight_force_update() when the backlight is changed using, for example,
> + * a hot-key. The updated brightness is read using get_brightness() and the
> + * brightness value is reported using an uevent.
>   */
>  void backlight_force_update(struct backlight_device *bd,
>  			    enum backlight_update_reason reason)
> @@ -336,19 +387,7 @@ void backlight_force_update(struct backlight_device *bd,
>  }
>  EXPORT_SYMBOL(backlight_force_update);
>  
> -/**
> - * backlight_device_register - create and register a new object of
> - *   backlight_device class.
> - * @name: the name of the new object(must be the same as the name of the
> - *   respective framebuffer device).
> - * @parent: a pointer to the parent device
> - * @devdata: an optional pointer to be stored for private driver use. The
> - *   methods may retrieve it by using bl_get_data(bd).
> - * @ops: the backlight operations structure.
> - *
> - * Creates and registers new backlight device. Returns either an
> - * ERR_PTR() or a pointer to the newly allocated device.
> - */
> +/* deprecated - use devm_backlight_device_register() */
>  struct backlight_device *backlight_device_register(const char *name,
>  	struct device *parent, void *devdata, const struct backlight_ops *ops,
>  	const struct backlight_properties *props)
> @@ -415,6 +454,15 @@ struct backlight_device *backlight_device_register(const char *name,
>  }
>  EXPORT_SYMBOL(backlight_device_register);
>  
> +/** backlight_device_get_by_type - find first backlight device of a type
> + * @type: the type of backlight device
> + *
> + * Look up the first backlight device of the specified type
> + *
> + * RETURNS:
> + *
> + * Pointer to backlight device if any was found. Otherwise NULL.
> + */
>  struct backlight_device *backlight_device_get_by_type(enum backlight_type type)
>  {
>  	bool found = false;
> @@ -433,12 +481,7 @@ struct backlight_device *backlight_device_get_by_type(enum backlight_type type)
>  }
>  EXPORT_SYMBOL(backlight_device_get_by_type);
>  
> -/**
> - * backlight_device_unregister - unregisters a backlight device object.
> - * @bd: the backlight device object to be unregistered and freed.
> - *
> - * Unregisters a previously registered via backlight_device_register object.
> - */
> +/* deprecated - use devm_backlight_device_unregister() */
>  void backlight_device_unregister(struct backlight_device *bd)
>  {
>  	if (!bd)
> @@ -486,10 +529,12 @@ static int devm_backlight_device_match(struct device *dev, void *res,
>   * backlight_register_notifier - get notified of backlight (un)registration
>   * @nb: notifier block with the notifier to call on backlight (un)registration
>   *
> - * @return 0 on success, otherwise a negative error code
> - *
>   * Register a notifier to get notified when backlight devices get registered
>   * or unregistered.
> + *
> + * RETURNS:
> + *
> + * 0 on success, otherwise a negative error code
>   */
>  int backlight_register_notifier(struct notifier_block *nb)
>  {
> @@ -501,10 +546,12 @@ EXPORT_SYMBOL(backlight_register_notifier);
>   * backlight_unregister_notifier - unregister a backlight notifier
>   * @nb: notifier block to unregister
>   *
> - * @return 0 on success, otherwise a negative error code
> - *
>   * Register a notifier to get notified when backlight devices get registered
>   * or unregistered.
> + *
> + * RETURNS:
> + *
> + * 0 on success, otherwise a negative error code
>   */
>  int backlight_unregister_notifier(struct notifier_block *nb)
>  {
> @@ -513,20 +560,22 @@ int backlight_unregister_notifier(struct notifier_block *nb)
>  EXPORT_SYMBOL(backlight_unregister_notifier);
>  
>  /**
> - * devm_backlight_device_register - resource managed backlight_device_register()
> + * devm_backlight_device_register - register a new backlight device
>   * @dev: the device to register
>   * @name: the name of the device
> - * @parent: a pointer to the parent device
> + * @parent: a pointer to the parent device (often the same as @dev)
>   * @devdata: an optional pointer to be stored for private driver use
>   * @ops: the backlight operations structure
>   * @props: the backlight properties
>   *
> - * @return a struct backlight on success, or an ERR_PTR on error
> + * Creates and registers new backlight device. When a backlight device
> + * is registered the configuration must be specified in the @props
> + * parameter. See description of &backlight_properties.
>   *
> - * Managed backlight_device_register(). The backlight_device returned
> - * from this function are automatically freed on driver detach.
> - * See backlight_device_register() for more information.
> - */
> + * RETURNS:
> + *
> + * struct backlight on success, or an ERR_PTR on error
> +*/
>  struct backlight_device *devm_backlight_device_register(struct device *dev,
>  	const char *name, struct device *parent, void *devdata,
>  	const struct backlight_ops *ops,
> @@ -553,13 +602,13 @@ struct backlight_device *devm_backlight_device_register(struct device *dev,
>  EXPORT_SYMBOL(devm_backlight_device_register);
>  
>  /**
> - * devm_backlight_device_unregister - resource managed backlight_device_unregister()
> + * devm_backlight_device_unregister - unregister backlight device
>   * @dev: the device to unregister
>   * @bd: the backlight device to unregister
>   *
> - * Deallocated a backlight allocated with devm_backlight_device_register().
> + * Deallocates a backlight allocated with devm_backlight_device_register().
>   * Normally this function will not need to be called and the resource management
> - * code will ensure that the resource is freed.
> + * code will ensure that the resources are freed.
>   */
>  void devm_backlight_device_unregister(struct device *dev,
>  				struct backlight_device *bd)
> @@ -650,8 +699,8 @@ static void devm_backlight_release(void *data)
>  }
>  
>  /**
> - * devm_of_find_backlight - Resource-managed of_find_backlight()
> - * @dev: Device
> + * devm_of_find_backlight - find backlight for a device
> + * @dev: the device
>   *
>   * Device managed version of of_find_backlight().
>   * The reference on the backlight device is automatically
> -- 
> 2.25.1
> 
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