Message-ID: <CAJZ5v0gPLvu4oo-K4LNCWYyRsnNKkY-0VWPDFZTarjoZHzFO6A@mail.gmail.com>
Date:   Wed, 6 Feb 2019 23:01:35 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Daniel Vetter <daniel.vetter@...ll.ch>
Cc:     DRI Development <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "C, Ramalingam" <ramalingam.c@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Russell King <rmk+kernel@....linux.org.uk>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Daniel Vetter <daniel.vetter@...el.com>
Subject: Re: [PATCH] component: Add documentation

On Wed, Feb 6, 2019 at 5:47 PM Daniel Vetter <daniel.vetter@...ll.ch> wrote:
>
> While typing these I think doing an s/component_master/aggregate/
> would be useful:
> - it's shorter :-)
> - I think component/aggregate is much more meaningful naming than
>   component/puppetmaster or something like that. At least to my
>   English ear "aggregate" emphasizes much more the "assemble a pile of
>   things into something bigger" aspect, and there's not really much
>   of a control hierarchy between aggregate and constituing components.
>
> But that's way more than a quick doc typing exercise ...
>
> Thanks to Ram for commenting on an initial draft of these docs.
>
> v2: Review from Rafael:
> - git add Documenation/driver-api/component.rst
> - lots of polish to the wording + spelling fixes.
>
> v3: Review from Russell:
> - s/framework/helper
> - clarify the documentation for component_match_add functions.
>
> Cc: "C, Ramalingam" <ramalingam.c@...el.com>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Russell King <rmk+kernel@....linux.org.uk>
> Cc: Rafael J. Wysocki <rafael@...nel.org>
> Cc: Jaroslav Kysela <perex@...ex.cz>
> Cc: Takashi Iwai <tiwai@...e.com>
> Cc: Rodrigo Vivi <rodrigo.vivi@...el.com>
> Cc: Jani Nikula <jani.nikula@...ux.intel.com>
> Signed-off-by: Daniel Vetter <daniel.vetter@...el.com>

Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

> ---
>  Documentation/driver-api/component.rst   |  17 ++++
>  Documentation/driver-api/device_link.rst |   3 +
>  Documentation/driver-api/index.rst       |   1 +
>  drivers/base/component.c                 | 107 ++++++++++++++++++++++-
>  include/linux/component.h                |  71 +++++++++++++++
>  5 files changed, 196 insertions(+), 3 deletions(-)
>  create mode 100644 Documentation/driver-api/component.rst
>
> diff --git a/Documentation/driver-api/component.rst b/Documentation/driver-api/component.rst
> new file mode 100644
> index 000000000000..2da4a8f20607
> --- /dev/null
> +++ b/Documentation/driver-api/component.rst
> @@ -0,0 +1,17 @@
> +======================================
> +Component Helper for Aggregate Drivers
> +======================================
> +
> +.. kernel-doc:: drivers/base/component.c
> +   :doc: overview
> +
> +
> +API
> +===
> +
> +.. kernel-doc:: include/linux/component.h
> +   :internal:
> +
> +.. kernel-doc:: drivers/base/component.c
> +   :export:
> +
> diff --git a/Documentation/driver-api/device_link.rst b/Documentation/driver-api/device_link.rst
> index d6763272e747..2d5919b2b337 100644
> --- a/Documentation/driver-api/device_link.rst
> +++ b/Documentation/driver-api/device_link.rst
> @@ -1,6 +1,9 @@
>  .. |struct dev_pm_domain| replace:: :c:type:`struct dev_pm_domain <dev_pm_domain>`
>  .. |struct generic_pm_domain| replace:: :c:type:`struct generic_pm_domain <generic_pm_domain>`
>
> +
> +.. _device_link:
> +
>  ============
>  Device links
>  ============
> diff --git a/Documentation/driver-api/index.rst b/Documentation/driver-api/index.rst
> index ab38ced66a44..c0b600ed9961 100644
> --- a/Documentation/driver-api/index.rst
> +++ b/Documentation/driver-api/index.rst
> @@ -22,6 +22,7 @@ available subsections can be seen below.
>     device_connection
>     dma-buf
>     device_link
> +   component
>     message-based
>     sound
>     frame-buffer
> diff --git a/drivers/base/component.c b/drivers/base/component.c
> index ddcea8739c12..f34d4b784709 100644
> --- a/drivers/base/component.c
> +++ b/drivers/base/component.c
> @@ -16,6 +16,32 @@
>  #include <linux/slab.h>
>  #include <linux/debugfs.h>
>
> +/**
> + * DOC: overview
> + *
> + * The component helper allows drivers to collect a pile of sub-devices,
> + * including their bound drivers, into an aggregate driver. Various subsystems
> + * already provide functions to get hold of such components, e.g.
> + * of_clk_get_by_name(). The component helper can be used when such a
> + * subsystem-specific way to find a device is not available: The component
> + * helper fills the niche of aggregate drivers for specific hardware, where
> + * further standardization into a subsystem would not be practical. The common
> + * example is when a logical device (e.g. a DRM display driver) is spread around
> + * the SoC on various component (scanout engines, blending blocks, transcoders
> + * for various outputs and so on).
> + *
> + * The component helper also doesn't solve runtime dependencies, e.g. for system
> + * suspend and resume operations. See also :ref:`device links<device_link>`.
> + *
> + * Components are registered using component_add() and unregistered with
> + * component_del(), usually from the driver's probe and disconnect functions.
> + *
> + * Aggregate drivers first assemble a component match list of what they need
> + * using component_match_add(). This is then registered as an aggregate driver
> + * using component_master_add_with_match(), and unregistered using
> + * component_master_del().
> + */
> +
>  struct component;
>
>  struct component_match_array {
> @@ -301,10 +327,25 @@ static int component_match_realloc(struct device *dev,
>         return 0;
>  }
>
> -/*
> - * Add a component to be matched, with a release function.
> +/**
> + * component_match_add_release - add a component match with release callback
> + * @master: device with the aggregate driver
> + * @matchptr: pointer to the list of component matches
> + * @release: release function for @compare_data
> + * @compare: compare function to match against all components
> + * @compare_data: opaque pointer passed to the @compare function
> + *
> + * This adds a new component match to the list stored in @matchptr, which the
> + * @master aggregate driver needs to function. The list of component matches
> + * pointed to by @matchptr must be initialized to NULL before adding the first
> + * match.
> + *
> + * The allocated match list in @matchptr is automatically released using devm
> + * actions, where upon @release will be called to free any references held by
> + * @compare_data, e.g. when @compare_data is a &device_node that must be
> + * released with of_node_put().
>   *
> - * The match array is first created or extended if necessary.
> + * See also component_match_add().
>   */
>  void component_match_add_release(struct device *master,
>         struct component_match **matchptr,
> @@ -367,6 +408,18 @@ static void free_master(struct master *master)
>         kfree(master);
>  }
>
> +/**
> + * component_master_add_with_match - register an aggregate driver
> + * @dev: device with the aggregate driver
> + * @ops: callbacks for the aggregate driver
> + * @match: component match list for the aggregate driver
> + *
> + * Registers a new aggregate driver consisting of the components added to @match
> + * by calling one of the component_match_add() functions. Once all components in
> + * @match are available, it will be assembled by calling
> + * &component_master_ops.bind from @ops. Must be unregistered by calling
> + * component_master_del().
> + */
>  int component_master_add_with_match(struct device *dev,
>         const struct component_master_ops *ops,
>         struct component_match *match)
> @@ -403,6 +456,15 @@ int component_master_add_with_match(struct device *dev,
>  }
>  EXPORT_SYMBOL_GPL(component_master_add_with_match);
>
> +/**
> + * component_master_del - unregister an aggregate driver
> + * @dev: device with the aggregate driver
> + * @ops: callbacks for the aggregate driver
> + *
> + * Unregisters an aggregate driver registered with
> + * component_master_add_with_match(). If necessary the aggregate driver is first
> + * disassembled by calling &component_master_ops.unbind from @ops.
> + */
>  void component_master_del(struct device *dev,
>         const struct component_master_ops *ops)
>  {
> @@ -430,6 +492,15 @@ static void component_unbind(struct component *component,
>         devres_release_group(component->dev, component);
>  }
>
> +/**
> + * component_unbind_all - unbind all component to an aggregate driver
> + * @master_dev: device with the aggregate driver
> + * @data: opaque pointer, passed to all components
> + *
> + * Unbinds all components to the aggregate @dev by passing @data to their
> + * &component_ops.unbind functions. Should be called from
> + * &component_master_ops.unbind.
> + */
>  void component_unbind_all(struct device *master_dev, void *data)
>  {
>         struct master *master;
> @@ -503,6 +574,15 @@ static int component_bind(struct component *component, struct master *master,
>         return ret;
>  }
>
> +/**
> + * component_bind_all - bind all component to an aggregate driver
> + * @master_dev: device with the aggregate driver
> + * @data: opaque pointer, passed to all components
> + *
> + * Binds all components to the aggregate @dev by passing @data to their
> + * &component_ops.bind functions. Should be called from
> + * &component_master_ops.bind.
> + */
>  int component_bind_all(struct device *master_dev, void *data)
>  {
>         struct master *master;
> @@ -537,6 +617,18 @@ int component_bind_all(struct device *master_dev, void *data)
>  }
>  EXPORT_SYMBOL_GPL(component_bind_all);
>
> +/**
> + * component_add - register a component
> + * @dev: component device
> + * @ops: component callbacks
> + *
> + * Register a new component for @dev. Functions in @ops will be called when the
> + * aggregate driver is ready to bind the overall driver by calling
> + * component_bind_all(). See also &struct component_ops.
> + *
> + * The component needs to be unregistered at driver unload/disconnect by calling
> + * component_del().
> + */
>  int component_add(struct device *dev, const struct component_ops *ops)
>  {
>         struct component *component;
> @@ -568,6 +660,15 @@ int component_add(struct device *dev, const struct component_ops *ops)
>  }
>  EXPORT_SYMBOL_GPL(component_add);
>
> +/**
> + * component_del - unregister a component
> + * @dev: component device
> + * @ops: component callbacks
> + *
> + * Unregister a component added with component_add(). If the component is bound
> + * into an aggregate driver, this will force the entire aggregate driver, including
> + * all its components, to be unbound.
> + */
>  void component_del(struct device *dev, const struct component_ops *ops)
>  {
>         struct component *c, *component = NULL;
> diff --git a/include/linux/component.h b/include/linux/component.h
> index e71fbbbc74e2..4911598b4c42 100644
> --- a/include/linux/component.h
> +++ b/include/linux/component.h
> @@ -4,11 +4,31 @@
>
>  #include <linux/stddef.h>
>
> +
>  struct device;
>
> +/**
> + * struct component_ops - callbacks for component drivers
> + *
> + * Components are registered with component_add() and unregistered with
> + * component_del().
> + */
>  struct component_ops {
> +       /**
> +        * @bind:
> +        *
> +        * Called through component_bind_all() when the aggregate driver is
> +        * ready to bind the overall driver.
> +        */
>         int (*bind)(struct device *comp, struct device *master,
>                     void *master_data);
> +       /**
> +        * @unbind:
> +        *
> +        * Called through component_unbind_all() when the aggregate driver is
> +        * ready to bind the overall driver, or when component_bind_all() fails
> +        * part-ways through and needs to unbind some already bound components.
> +        */
>         void (*unbind)(struct device *comp, struct device *master,
>                        void *master_data);
>  };
> @@ -21,8 +41,42 @@ void component_unbind_all(struct device *master, void *master_data);
>
>  struct master;
>
> +/**
> + * struct component_master_ops - callback for the aggregate driver
> + *
> + * Aggregate drivers are registered with component_master_add_with_match() and
> + * unregistered with component_master_del().
> + */
>  struct component_master_ops {
> +       /**
> +        * @bind:
> +        *
> +        * Called when all components or the aggregate driver, as specified in
> +        * the match list passed to component_master_add_with_match(), are
> +        * ready. Usually there are 3 steps to bind an aggregate driver:
> +        *
> +        * 1. Allocate a structure for the aggregate driver.
> +        *
> +        * 2. Bind all components to the aggregate driver by calling
> +        *    component_bind_all() with the aggregate driver structure as opaque
> +        *    pointer data.
> +        *
> +        * 3. Register the aggregate driver with the subsystem to publish its
> +        *    interfaces.
> +        *
> +        * Note that the lifetime of the aggregate driver does not align with
> +        * any of the underlying &struct device instances. Therefore devm cannot
> +        * be used and all resources acquired or allocated in this callback must
> +        * be explicitly released in the @unbind callback.
> +        */
>         int (*bind)(struct device *master);
> +       /**
> +        * @unbind:
> +        *
> +        * Called when either the aggregate driver, using
> +        * component_master_del(), or one of its components, using
> +        * component_del(), is unregistered.
> +        */
>         void (*unbind)(struct device *master);
>  };
>
> @@ -38,6 +92,23 @@ void component_match_add_release(struct device *master,
>         void (*release)(struct device *, void *),
>         int (*compare)(struct device *, void *), void *compare_data);
>
> +/**
> + * component_match_add - add a compent match
> + * @master: device with the aggregate driver
> + * @matchptr: pointer to the list of component matches
> + * @compare: compare function to match against all components
> + * @compare_data: opaque pointer passed to the @compare function
> + *
> + * This adds a new component match to the list stored in @matchptr, which the
> + * @master aggregate driver needs to function. The list of component matches
> + * pointed to by @matchptr must be initialized to NULL before adding the first
> + * match.
> + *
> + * The allocated match list in @matchptr is automatically released using devm
> + * actions.
> + *
> + * See also component_match_add_release().
> + */
>  static inline void component_match_add(struct device *master,
>         struct component_match **matchptr,
>         int (*compare)(struct device *, void *), void *compare_data)
> --
> 2.20.1
>

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