Date:   Fri,  3 Nov 2023 16:45:22 +1030
From:   Andrew Jeffery <andrew@...econstruct.com.au>
To:     minyard@....org, openipmi-developer@...ts.sourceforge.net
Cc:     Andrew Jeffery <andrew@...econstruct.com.au>,
        linux-kernel@...r.kernel.org, Jonathan.Cameron@...wei.com,
        aladyshev22@...il.com, jk@...econstruct.com.au
Subject: [PATCH 10/10] ipmi: kcs_bmc: Add subsystem kerneldoc

Provide kerneldoc describing the relationships between and the
behaviours of the structures and functions of the KCS subsystem.

Signed-off-by: Andrew Jeffery <andrew@...econstruct.com.au>
---
 drivers/char/ipmi/kcs_bmc.h        |  39 ++++++++
 drivers/char/ipmi/kcs_bmc_client.h | 151 +++++++++++++++++++++++++++++
 drivers/char/ipmi/kcs_bmc_device.h |  40 ++++++++
 3 files changed, 230 insertions(+)

diff --git a/drivers/char/ipmi/kcs_bmc.h b/drivers/char/ipmi/kcs_bmc.h
index 979d673f8f56..69eee539ec50 100644
--- a/drivers/char/ipmi/kcs_bmc.h
+++ b/drivers/char/ipmi/kcs_bmc.h
@@ -10,6 +10,36 @@
 #include <linux/module.h>
 #include <linux/spinlock.h>
 
+/**
+ * DOC: KCS subsystem structure
+ *
+ * The KCS subsystem is split into three components:
+ *
+ * 1. &struct kcs_bmc_device
+ * 2. &struct kcs_bmc_driver
+ * 3. &struct kcs_bmc_client
+ *
+ * ``struct kcs_bmc_device`` (device) represents a driver instance for a
+ * particular KCS device. ``struct kcs_bmc_device``` abstracts away the device
+ * specifics allowing for device-independent implementation of protocols over
+ * KCS.
+ *
+ * ``struct kcs_bmc_driver`` (driver) represents an implementation of a KCS
+ * protocol. Implementations of a protocol either expose this behaviour out to
+ * userspace via a character device, or provide the glue into another kernel
+ * subsystem.
+ *
+ * ``struct kcs_bmc_client`` (client) associates a ``struct kcs_bmc_device``
+ * instance (``D``) with a &struct kcs_bmc_driver instance (``P``). An instance
+ * of each protocol implementation is associated with each device, yielding
+ * ``D*P`` client instances.
+ *
+ * A device may only have one active client at a time. A client becomes active
+ * on its associated device whenever userspace "opens" its interface in some
+ * fashion, for example, opening a character device. If the device associated
+ * with a client already has an active client then an error is propagated.
+ */
+
 #define KCS_BMC_EVENT_TYPE_OBE	BIT(0)
 #define KCS_BMC_EVENT_TYPE_IBF	BIT(1)
 
@@ -31,6 +61,15 @@ struct kcs_ioreg {
 struct kcs_bmc_device_ops;
 struct kcs_bmc_client;
 
+/**
+ * struct kcs_bmc_device - An abstract representation of a KCS device
+ * @entry: A list node for the KCS core to track KCS device instances
+ * @dev: The kernel device object for the KCS hardware
+ * @channel: The IPMI channel number for the KCS device
+ * @ops: A set of callbacks for providing abstract access to the KCS hardware
+ * @lock: Protects accesses to, and operations on &kcs_bmc_device.client
+ * @client: The client instance, if any, currently associated with the device
+ */
 struct kcs_bmc_device {
 	struct list_head entry;
 
diff --git a/drivers/char/ipmi/kcs_bmc_client.h b/drivers/char/ipmi/kcs_bmc_client.h
index afc9e71c9fc0..8ccaaf10c10e 100644
--- a/drivers/char/ipmi/kcs_bmc_client.h
+++ b/drivers/char/ipmi/kcs_bmc_client.h
@@ -11,10 +11,24 @@
 
 struct kcs_bmc_driver;
 
+/**
+ * struct kcs_bmc_client_ops - Callbacks operating on a client instance
+ * @event: A notification to the client that the device has an active interrupt
+ */
 struct kcs_bmc_client_ops {
 	irqreturn_t (*event)(struct kcs_bmc_client *client);
 };
 
+/**
+ * struct kcs_bmc_client - Associates a KCS protocol implementation with a KCS device
+ * @ops: A set of callbacks for handling client events
+ * @drv: The KCS protocol implementation associated with the client instance
+ * @dev: The KCS device instance associated with the client instance
+ * @entry: A list node for the KCS core to track KCS client instances
+ *
+ * A ``struct kcs_bmc_client`` should be created for each device added via
+ * &kcs_bmc_driver_ops.add_device
+ */
 struct kcs_bmc_client {
 	const struct kcs_bmc_client_ops *ops;
 
@@ -23,12 +37,32 @@ struct kcs_bmc_client {
 	struct list_head entry;
 };
 
+/**
+ * struct kcs_bmc_driver_ops - KCS device lifecycle operations for a KCS protocol driver
+ * @add_device: A new device has appeared, a client instance is to be created
+ * @remove_device: A known device has been removed - a client instance should be destroyed
+ */
 struct kcs_bmc_driver_ops {
 	struct kcs_bmc_client *(*add_device)(struct kcs_bmc_driver *drv,
 					     struct kcs_bmc_device *dev);
 	void (*remove_device)(struct kcs_bmc_client *client);
 };
 
+/**
+ * kcs_bmc_client_init() - Initialise an instance of &struct kcs_bmc_client
+ * @client: The &struct kcs_bmc_client instance of interest, usually embedded in
+ *          an instance-private struct
+ * @ops: The &struct kcs_bmc_client_ops relevant for @client
+ * @drv: The &struct kcs_bmc_driver instance relevant for @client
+ * @dev: The &struct kcs_bmc_device instance relevant for @client
+ *
+ * It's intended that kcs_bmc_client_init() is invoked in the @add_device
+ * callback for the protocol driver where the protocol-private data is
+ * initialised for the new device instance. The function is provided to make
+ * sure that all required fields are initialised.
+ *
+ * Context: Any context
+ */
 static inline void kcs_bmc_client_init(struct kcs_bmc_client *client,
 				       const struct kcs_bmc_client_ops *ops,
 				       struct kcs_bmc_driver *drv,
@@ -39,24 +73,141 @@ static inline void kcs_bmc_client_init(struct kcs_bmc_client *client,
 	client->dev = dev;
 }
 
+/**
+ * struct kcs_bmc_driver - An implementation of a protocol run over a KCS channel
+ * @entry: A list node for the KCS core to track KCS protocol drivers
+ * @ops: A set of callbacks for handling device lifecycle events for the protocol driver
+ */
 struct kcs_bmc_driver {
 	struct list_head entry;
 
 	const struct kcs_bmc_driver_ops *ops;
 };
 
+/**
+ * kcs_bmc_register_driver() - Register a KCS protocol driver with the KCS subsystem
+ * @drv: The &struct kcs_bmc_driver instance to register
+ *
+ * Generally only invoked on module init.
+ *
+ * Context: Process context. Takes and releases the internal KCS subsystem mutex.
+ *
+ * Return: 0 on succes.
+ */
 int kcs_bmc_register_driver(struct kcs_bmc_driver *drv);
+
+/**
+ * kcs_bmc_unregister_driver() - Unregister a KCS protocol driver with the KCS
+ *                               subsystem
+ * @drv: The &struct kcs_bmc_driver instance to unregister
+ *
+ * Generally only invoked on module exit.
+ *
+ * Context: Process context. Takes and releases the internal KCS subsystem mutex.
+ */
 void kcs_bmc_unregister_driver(struct kcs_bmc_driver *drv);
 
+/**
+ * module_kcs_bmc_driver() - Helper macro for registering a module KCS protocol driver
+ * @__kcs_bmc_driver: A ``struct kcs_bmc_driver``
+ *
+ * Helper macro for KCS protocol drivers which do not do anything special in
+ * module init/exit. This eliminates a lot of boilerplate. Each module may only
+ * use this macro once, and calling it replaces module_init() and module_exit()
+ */
 #define module_kcs_bmc_driver(__kcs_bmc_driver) \
 	module_driver(__kcs_bmc_driver, kcs_bmc_register_driver, \
 		kcs_bmc_unregister_driver)
 
+/**
+ * kcs_bmc_enable_device() - Prepare a KCS device for active use
+ * @client: The client whose KCS device should be enabled
+ *
+ * A client should enable its associated KCS device when the userspace
+ * interface for the client is "opened" in some fashion. Enabling the KCS device
+ * associates the client with the device and enables interrupts on the hardware.
+ *
+ * Context: Process context. Takes and releases ``client->dev->lock``
+ *
+ * Return: 0 on success, or -EBUSY if a client is already associated with the
+ *         device
+ */
 int kcs_bmc_enable_device(struct kcs_bmc_client *client);
+
+/**
+ * kcs_bmc_disable_device() - Remove a KCS device from active use
+ * @client: The client whose KCS device should be disabled
+ *
+ * A client should disable its associated KCS device when the userspace
+ * interface for the client is "closed" in some fashion. The client is
+ * disassociated from the device iff it was the active client. If the client is
+ * disassociated then interrupts are disabled on the hardware.
+ *
+ * Context: Process context. Takes and releases ``client->dev->lock``.
+ */
 void kcs_bmc_disable_device(struct kcs_bmc_client *client);
+
+/**
+ * kcs_bmc_read_data() - Read the Input Data Register (IDR) on a KCS device
+ * @client: The client whose device's IDR should be read
+ *
+ * Must only be called on a client that is currently active on its associated
+ * device.
+ *
+ * Context: Any context. Any spinlocks taken are also released.
+ *
+ * Return: The value of IDR
+ */
 u8 kcs_bmc_read_data(struct kcs_bmc_client *client);
+
+/**
+ * kcs_bmc_write_data() - Write the Output Data Register (ODR) on a KCS device
+ * @client: The client whose device's ODR should be written
+ * @data: The value to write to ODR
+ *
+ * Must only be called on a client that is currently active on its associated
+ * device.
+ *
+ * Context: Any context. Any spinlocks taken are also released.
+ */
 void kcs_bmc_write_data(struct kcs_bmc_client *client, u8 data);
+
+/**
+ * kcs_bmc_read_status() - Read the Status Register (STR) on a KCS device
+ * @client: The client whose device's STR should be read
+ *
+ * Must only be called on a client that is currently active on its associated
+ * device.
+ *
+ * Context: Any context. Any spinlocks taken are also released.
+ *
+ * Return: The value of STR
+ */
 u8 kcs_bmc_read_status(struct kcs_bmc_client *client);
+
+/**
+ * kcs_bmc_write_status() - Write the Status Register (STR) on a KCS device
+ * @client: The client whose device's STR should be written
+ * @data: The value to write to STR
+ *
+ * Must only be called on a client that is currently active on its associated
+ * device.
+ *
+ * Context: Any context. Any spinlocks taken are also released.
+ */
 void kcs_bmc_write_status(struct kcs_bmc_client *client, u8 data);
+
+/**
+ * kcs_bmc_update_status() - Update Status Register (STR) on a KCS device
+ * @client: The client whose device's STR should be updated
+ * @mask: A bit-mask defining the field in STR that should be updated
+ * @val: The new value of the field, specified in the position of the bit-mask
+ *       defined by @mask
+ *
+ * Must only be called on a client that is currently active on its associated
+ * device.
+ *
+ * Context: Any context. Any spinlocks taken are also released.
+ */
 void kcs_bmc_update_status(struct kcs_bmc_client *client, u8 mask, u8 val);
 #endif
diff --git a/drivers/char/ipmi/kcs_bmc_device.h b/drivers/char/ipmi/kcs_bmc_device.h
index ca2b5dc2031d..b17171d1c981 100644
--- a/drivers/char/ipmi/kcs_bmc_device.h
+++ b/drivers/char/ipmi/kcs_bmc_device.h
@@ -8,6 +8,13 @@
 
 #include "kcs_bmc.h"
 
+/**
+ * struct kcs_bmc_device_ops - Callbacks operating on a KCS device
+ * @irq_mask_update: Update the set of events of interest
+ * @io_inputb: A callback to read the specified KCS register from hardware
+ * @io_outputb: A callback to write the specified KCS register to hardware
+ * @io_updateb: A callback to update a subfield of the specified KCS register
+ */
 struct kcs_bmc_device_ops {
 	void (*irq_mask_update)(struct kcs_bmc_device *kcs_bmc, u8 mask, u8 enable);
 	u8 (*io_inputb)(struct kcs_bmc_device *kcs_bmc, u32 reg);
@@ -15,8 +22,41 @@ struct kcs_bmc_device_ops {
 	void (*io_updateb)(struct kcs_bmc_device *kcs_bmc, u32 reg, u8 mask, u8 b);
 };
 
+/**
+ * kcs_bmc_handle_event() - Notify the active client of a hardware interrupt
+ * @kcs_bmc: The device instance whose interrupt was triggered
+ *
+ * Propagate a hardware interrupt as an event to the active client. The client's
+ * handler should take any necessary actions for the protocol it implements, but
+ * must read IDR to resolve the interrupt if the interrupt was generated by the
+ * KCS device.
+ *
+ * Context: Interrupt context. Takes and releases &kcs_bmc_device.lock.
+ *
+ * Return: An irqreturn_t value indicating whether the interrupt was handled.
+ */
 irqreturn_t kcs_bmc_handle_event(struct kcs_bmc_device *kcs_bmc);
+
+/**
+ * kcs_bmc_add_device() - Register a KCS device instance with the KCS subsystem
+ * @dev: The &struct kcs_bmc_device instance to register
+ *
+ * Should be called by the probe() implementation of the KCS hardware's driver.
+ *
+ * Context: Process context. Takes and releases the internal KCS subsystem mutex.
+ *
+ * Return: 0 on success, or a negative errno on failure.
+ */
 int kcs_bmc_add_device(struct kcs_bmc_device *dev);
+
+/**
+ * kcs_bmc_remove_device() - Unregister a KCS device instance with the KCS subsystem
+ * @dev: The &struct kcs_bmc_device instance to unregister
+ *
+ * Should be called by the remove() implementation of the KCS hardware's driver.
+ *
+ * Context: Process context. Takes and releases the internal KCS subsystem mutex.
+ */
 void kcs_bmc_remove_device(struct kcs_bmc_device *dev);
 
 #endif
-- 
2.39.2

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