[PATCH 1/3] component: Add documentation

Daniel Vetter
2019-02-06T16:46:09Z

Someone owes me a beer ...

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@intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Cc: Rafael J. Wysocki <rafael@kernel.org>
Cc: Jaroslav Kysela <perex@perex.cz>
Cc: Takashi Iwai <tiwai@suse.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.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