dm: Add base driver model support

Add driver model functionality for generic board.

This includes data structures and base code for registering devices and
uclasses (groups of devices with the same purpose, e.g. all I2C ports will
be in the same uclass).

The feature is enabled with CONFIG_DM.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Marek Vasut <marex@denx.de>
Signed-off-by: Pavel Herrmann <morpheus.ibis@gmail.com>
Signed-off-by: Viktor Křivák <viktor.krivak@gmail.com>
Signed-off-by: Tomas Hlavacek <tmshlvck@gmail.com>

11 files changed, 666 insertions, 0 deletions

diff --git a/include/asm-generic/global_data.h b/include/asm-generic/global_data.h
index 0de0bea..707400e 100644
--- a/include/asm-generic/global_data.h
+++ b/include/asm-generic/global_data.h
@@ -21,6 +21,8 @@
  */
 
 #ifndef __ASSEMBLY__
+#include <linux/list.h>
+
 typedef struct global_data {
 	bd_t *bd;
 	unsigned long flags;
@@ -61,6 +63,12 @@ typedef struct global_data {
 	unsigned long start_addr_sp;	/* start_addr_stackpointer */
 	unsigned long reloc_off;
 	struct global_data *new_gd;	/* relocated global data */
+
+#ifdef CONFIG_DM
+	struct device	*dm_root;	/* Root instance for Driver Model */
+	struct list_head uclass_root;	/* Head of core tree */
+#endif
+
 	const void *fdt_blob;	/* Our device tree, NULL if none */
 	void *new_fdt;		/* Relocated FDT */
 	unsigned long fdt_size;	/* Space reserved for relocated FDT */
diff --git a/include/dm.h b/include/dm.h
new file mode 100644
index 0000000..8bbb21b
--- /dev/null
+++ b/include/dm.h
@@ -0,0 +1,14 @@
+/*
+ * Copyright (c) 2013 Google, Inc
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef _DM_H_
+#define _DM_H
+
+#include <dm/device.h>
+#include <dm/platdata.h>
+#include <dm/uclass.h>
+
+#endif
diff --git a/include/dm/device-internal.h b/include/dm/device-internal.h
new file mode 100644
index 0000000..c026e8e
--- /dev/null
+++ b/include/dm/device-internal.h
@@ -0,0 +1,87 @@
+/*
+ * Copyright (C) 2013 Google, Inc
+ *
+ * (C) Copyright 2012
+ * Pavel Herrmann <morpheus.ibis@gmail.com>
+ * Marek Vasut <marex@denx.de>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef _DM_DEVICE_INTERNAL_H
+#define _DM_DEVICE_INTERNAL_H
+
+struct device;
+
+/**
+ * device_bind() - Create a device and bind it to a driver
+ *
+ * Called to set up a new device attached to a driver. The device will either
+ * have platdata, or a device tree node which can be used to create the
+ * platdata.
+ *
+ * Once bound a device exists but is not yet active until device_probe() is
+ * called.
+ *
+ * @parent: Pointer to device's parent, under which this driver will exist
+ * @drv: Device's driver
+ * @name: Name of device (e.g. device tree node name)
+ * @platdata: Pointer to data for this device - the structure is device-
+ * specific but may include the device's I/O address, etc.. This is NULL for
+ * devices which use device tree.
+ * @of_offset: Offset of device tree node for this device. This is -1 for
+ * devices which don't use device tree.
+ * @devp: Returns a pointer to the bound device
+ * @return 0 if OK, -ve on error
+ */
+int device_bind(struct device *parent, struct driver *drv,
+		const char *name, void *platdata, int of_offset,
+		struct device **devp);
+
+/**
+ * device_bind_by_name: Create a device and bind it to a driver
+ *
+ * This is a helper function used to bind devices which do not use device
+ * tree.
+ *
+ * @parent: Pointer to device's parent
+ * @info: Name and platdata for this device
+ * @devp: Returns a pointer to the bound device
+ * @return 0 if OK, -ve on error
+ */
+int device_bind_by_name(struct device *parent, const struct driver_info *info,
+			struct device **devp);
+
+/**
+ * device_probe() - Probe a device, activating it
+ *
+ * Activate a device so that it is ready for use. All its parents are probed
+ * first.
+ *
+ * @dev: Pointer to device to probe
+ * @return 0 if OK, -ve on error
+ */
+int device_probe(struct device *dev);
+
+/**
+ * device_remove() - Remove a device, de-activating it
+ *
+ * De-activate a device so that it is no longer ready for use. All its
+ * children are deactivated first.
+ *
+ * @dev: Pointer to device to remove
+ * @return 0 if OK, -ve on error (an error here is normally a very bad thing)
+ */
+int device_remove(struct device *dev);
+
+/**
+ * device_unbind() - Unbind a device, destroying it
+ *
+ * Unbind a device and remove all memory used by it
+ *
+ * @dev: Pointer to device to unbind
+ * @return 0 if OK, -ve on error
+ */
+int device_unbind(struct device *dev);
+
+#endif
diff --git a/include/dm/device.h b/include/dm/device.h
new file mode 100644
index 0000000..4cd38ed
--- /dev/null
+++ b/include/dm/device.h
@@ -0,0 +1,159 @@
+/*
+ * Copyright (c) 2013 Google, Inc
+ *
+ * (C) Copyright 2012
+ * Pavel Herrmann <morpheus.ibis@gmail.com>
+ * Marek Vasut <marex@denx.de>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef _DM_DEVICE_H
+#define _DM_DEVICE_H
+
+#include <dm/uclass-id.h>
+#include <linker_lists.h>
+#include <linux/list.h>
+
+struct driver_info;
+
+/* Driver is active (probed). Cleared when it is removed */
+#define DM_FLAG_ACTIVATED	(1 << 0)
+
+/* DM is responsible for allocating and freeing platdata */
+#define DM_FLAG_ALLOC_PDATA	(2 << 0)
+
+/**
+ * struct device - An instance of a driver
+ *
+ * This holds information about a device, which is a driver bound to a
+ * particular port or peripheral (essentially a driver instance).
+ *
+ * A device will come into existence through a 'bind' call, either due to
+ * a U_BOOT_DEVICE() macro (in which case platdata is non-NULL) or a node
+ * in the device tree (in which case of_offset is >= 0). In the latter case
+ * we translate the device tree information into platdata in a function
+ * implemented by the driver ofdata_to_platdata method (called just before the
+ * probe method if the device has a device tree node.
+ *
+ * All three of platdata, priv and uclass_priv can be allocated by the
+ * driver, or you can use the auto_alloc_size members of struct driver and
+ * struct uclass_driver to have driver model do this automatically.
+ *
+ * @driver: The driver used by this device
+ * @name: Name of device, typically the FDT node name
+ * @platdata: Configuration data for this device
+ * @of_offset: Device tree node offset for this device (- for none)
+ * @parent: Parent of this device, or NULL for the top level device
+ * @priv: Private data for this device
+ * @uclass: Pointer to uclass for this device
+ * @uclass_priv: The uclass's private data for this device
+ * @uclass_node: Used by uclass to link its devices
+ * @child_head: List of children of this device
+ * @sibling_node: Next device in list of all devices
+ * @flags: Flags for this device DM_FLAG_...
+ */
+struct device {
+	struct driver *driver;
+	const char *name;
+	void *platdata;
+	int of_offset;
+	struct device *parent;
+	void *priv;
+	struct uclass *uclass;
+	void *uclass_priv;
+	struct list_head uclass_node;
+	struct list_head child_head;
+	struct list_head sibling_node;
+	uint32_t flags;
+};
+
+/* Returns the operations for a device */
+#define device_get_ops(dev)	(dev->driver->ops)
+
+/* Returns non-zero if the device is active (probed and not removed) */
+#define device_active(dev)	((dev)->flags & DM_FLAG_ACTIVATED)
+
+/**
+ * struct device_id - Lists the compatible strings supported by a driver
+ * @compatible: Compatible string
+ * @data: Data for this compatible string
+ */
+struct device_id {
+	const char *compatible;
+	ulong data;
+};
+
+/**
+ * struct driver - A driver for a feature or peripheral
+ *
+ * This holds methods for setting up a new device, and also removing it.
+ * The device needs information to set itself up - this is provided either
+ * by platdata or a device tree node (which we find by looking up
+ * matching compatible strings with of_match).
+ *
+ * Drivers all belong to a uclass, representing a class of devices of the
+ * same type. Common elements of the drivers can be implemented in the uclass,
+ * or the uclass can provide a consistent interface to the drivers within
+ * it.
+ *
+ * @name: Device name
+ * @id: Identiies the uclass we belong to
+ * @of_match: List of compatible strings to match, and any identifying data
+ * for each.
+ * @bind: Called to bind a device to its driver
+ * @probe: Called to probe a device, i.e. activate it
+ * @remove: Called to remove a device, i.e. de-activate it
+ * @unbind: Called to unbind a device from its driver
+ * @ofdata_to_platdata: Called before probe to decode device tree data
+ * @priv_auto_alloc_size: If non-zero this is the size of the private data
+ * to be allocated in the device's ->priv pointer. If zero, then the driver
+ * is responsible for allocating any data required.
+ * @platdata_auto_alloc_size: If non-zero this is the size of the
+ * platform data to be allocated in the device's ->platdata pointer.
+ * This is typically only useful for device-tree-aware drivers (those with
+ * an of_match), since drivers which use platdata will have the data
+ * provided in the U_BOOT_DEVICE() instantiation.
+ * ops: Driver-specific operations. This is typically a list of function
+ * pointers defined by the driver, to implement driver functions required by
+ * the uclass.
+ */
+struct driver {
+	char *name;
+	enum uclass_id id;
+	const struct device_id *of_match;
+	int (*bind)(struct device *dev);
+	int (*probe)(struct device *dev);
+	int (*remove)(struct device *dev);
+	int (*unbind)(struct device *dev);
+	int (*ofdata_to_platdata)(struct device *dev);
+	int priv_auto_alloc_size;
+	int platdata_auto_alloc_size;
+	const void *ops;	/* driver-specific operations */
+};
+
+/* Declare a new U-Boot driver */
+#define U_BOOT_DRIVER(__name)						\
+	ll_entry_declare(struct driver, __name, driver)
+
+/**
+ * dev_get_platdata() - Get the platform data for a device
+ *
+ * This checks that dev is not NULL, but no other checks for now
+ *
+ * @dev		Device to check
+ * @return platform data, or NULL if none
+ */
+void *dev_get_platdata(struct device *dev);
+
+/**
+ * dev_get_priv() - Get the private data for a device
+ *
+ * This checks that dev is not NULL, but no other checks for now
+ *
+ * @dev		Device to check
+ * @return private data, or NULL if none
+ */
+void *dev_get_priv(struct device *dev);
+
+#endif
diff --git a/include/dm/lists.h b/include/dm/lists.h
new file mode 100644
index 0000000..0d09f9a
--- /dev/null
+++ b/include/dm/lists.h
@@ -0,0 +1,39 @@
+/*
+ * Copyright (c) 2013 Google, Inc
+ *
+ * (C) Copyright 2012
+ * Pavel Herrmann <morpheus.ibis@gmail.com>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef _DM_LISTS_H_
+#define _DM_LISTS_H_
+
+#include <dm/uclass-id.h>
+
+/**
+ * lists_driver_lookup_name() - Return u_boot_driver corresponding to name
+ *
+ * This function returns a pointer to a driver given its name. This is used
+ * for binding a driver given its name and platdata.
+ *
+ * @name: Name of driver to look up
+ * @return pointer to driver, or NULL if not found
+ */
+struct driver *lists_driver_lookup_name(const char *name);
+
+/**
+ * lists_uclass_lookup() - Return uclass_driver based on ID of the class
+ * id:		ID of the class
+ *
+ * This function returns the pointer to uclass_driver, which is the class's
+ * base structure based on the ID of the class. Returns NULL on error.
+ */
+struct uclass_driver *lists_uclass_lookup(enum uclass_id id);
+
+int lists_bind_drivers(struct device *parent);
+
+int lists_bind_fdt(struct device *parent, const void *blob, int offset);
+
+#endif
diff --git a/include/dm/platdata.h b/include/dm/platdata.h
new file mode 100644
index 0000000..0ef3353
--- /dev/null
+++ b/include/dm/platdata.h
@@ -0,0 +1,22 @@
+/*
+ * Copyright (c) 2013 Google, Inc
+ *
+ * (C) Copyright 2012
+ * Pavel Herrmann <morpheus.ibis@gmail.com>
+ * Marek Vasut <marex@denx.de>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef _DM_PLATDATA_H
+#define _DM_PLATDATA_H
+
+struct driver_info {
+	const char	*name;
+	const void	*platdata;
+};
+
+#define U_BOOT_DEVICE(__name)						\
+	ll_entry_declare(struct driver_info, __name, driver_info)
+
+#endif
diff --git a/include/dm/root.h b/include/dm/root.h
new file mode 100644
index 0000000..0ebccda
--- /dev/null
+++ b/include/dm/root.h
@@ -0,0 +1,53 @@
+/*
+ * Copyright (c) 2013 Google, Inc
+ *
+ * (C) Copyright 2012
+ * Pavel Herrmann <morpheus.ibis@gmail.com>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef _DM_ROOT_H_
+#define _DM_ROOT_H_
+
+struct device;
+
+/**
+ * dm_root() - Return pointer to the top of the driver tree
+ *
+ * This function returns pointer to the root node of the driver tree,
+ *
+ * @return pointer to root device, or NULL if not inited yet
+ */
+struct device *dm_root(void);
+
+/**
+ * dm_scan_platdata() - Scan all platform data and bind drivers
+ *
+ * This scans all available platdata and creates drivers for each
+ *
+ * @return 0 if OK, -ve on error
+ */
+int dm_scan_platdata(void);
+
+/**
+ * dm_scan_fdt() - Scan the device tree and bind drivers
+ *
+ * This scans the device tree and creates a driver for each node
+ *
+ * @blob: Pointer to device tree blob
+ * @return 0 if OK, -ve on error
+ */
+int dm_scan_fdt(const void *blob);
+
+/**
+ * dm_init() - Initialize Driver Model structures
+ *
+ * This function will initialize roots of driver tree and class tree.
+ * This needs to be called before anything uses the DM
+ *
+ * @return 0 if OK, -ve on error
+ */
+int dm_init(void);
+
+#endif
diff --git a/include/dm/uclass-id.h b/include/dm/uclass-id.h
new file mode 100644
index 0000000..f0e691c
--- /dev/null
+++ b/include/dm/uclass-id.h
@@ -0,0 +1,28 @@
+/*
+ * Copyright (c) 2013 Google, Inc
+ *
+ * (C) Copyright 2012
+ * Pavel Herrmann <morpheus.ibis@gmail.com>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef _DM_UCLASS_ID_H
+#define _DM_UCLASS_ID_H
+
+/* TODO(sjg@chromium.org): this could be compile-time generated */
+enum uclass_id {
+	/* These are used internally by driver model */
+	UCLASS_ROOT = 0,
+	UCLASS_DEMO,
+	UCLASS_TEST,
+	UCLASS_TEST_FDT,
+
+	/* U-Boot uclasses start here */
+	UCLASS_GPIO,
+
+	UCLASS_COUNT,
+	UCLASS_INVALID = -1,
+};
+
+#endif
diff --git a/include/dm/uclass-internal.h b/include/dm/uclass-internal.h
new file mode 100644
index 0000000..cc65d52
--- /dev/null
+++ b/include/dm/uclass-internal.h
@@ -0,0 +1,85 @@
+/*
+ * Copyright (c) 2013 Google, Inc
+ *
+ * (C) Copyright 2012
+ * Pavel Herrmann <morpheus.ibis@gmail.com>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef _DM_UCLASS_INTERNAL_H
+#define _DM_UCLASS_INTERNAL_H
+
+/**
+ * uclass_find_device() - Return n-th child of uclass
+ * @id:		Id number of the uclass
+ * @index:	Position of the child in uclass's list
+ * #devp:	Returns pointer to device, or NULL on error
+ *
+ * The device is not prepared for use - this is an internal function
+ *
+ * @return the uclass pointer of a child at the given index or
+ * return NULL on error.
+ */
+int uclass_find_device(enum uclass_id id, int index, struct device **devp);
+
+/**
+ * uclass_bind_device() - Associate device with a uclass
+ *
+ * Connect the device into uclass's list of devices.
+ *
+ * @dev:	Pointer to the device
+ * #return 0 on success, -ve on error
+ */
+int uclass_bind_device(struct device *dev);
+
+/**
+ * uclass_unbind_device() - Deassociate device with a uclass
+ *
+ * Disconnect the device from uclass's list of devices.
+ *
+ * @dev:	Pointer to the device
+ * #return 0 on success, -ve on error
+ */
+int uclass_unbind_device(struct device *dev);
+
+/**
+ * uclass_post_probe_device() - Deal with a device that has just been probed
+ *
+ * Perform any post-processing of a probed device that is needed by the
+ * uclass.
+ *
+ * @dev:	Pointer to the device
+ * #return 0 on success, -ve on error
+ */
+int uclass_post_probe_device(struct device *dev);
+
+/**
+ * uclass_pre_remove_device() - Handle a device which is about to be removed
+ *
+ * Perform any pre-processing of a device that is about to be removed.
+ *
+ * @dev:	Pointer to the device
+ * #return 0 on success, -ve on error
+ */
+int uclass_pre_remove_device(struct device *dev);
+
+/**
+ * uclass_find() - Find uclass by its id
+ *
+ * @id:		Id to serach for
+ * @return pointer to uclass, or NULL if not found
+ */
+struct uclass *uclass_find(enum uclass_id key);
+
+/**
+ * uclass_destroy() - Destroy a uclass
+ *
+ * Destroy a uclass and all its devices
+ *
+ * @uc: uclass to destroy
+ * @return 0 on success, -ve on error
+ */
+int uclass_destroy(struct uclass *uc);
+
+#endif
diff --git a/include/dm/uclass.h b/include/dm/uclass.h
new file mode 100644
index 0000000..cd23cfe
--- /dev/null
+++ b/include/dm/uclass.h
@@ -0,0 +1,142 @@
+/*
+ * Copyright (c) 2013 Google, Inc
+ *
+ * (C) Copyright 2012
+ * Pavel Herrmann <morpheus.ibis@gmail.com>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef _DM_UCLASS_H
+#define _DM_UCLASS_H
+
+#include <dm/uclass-id.h>
+#include <linux/list.h>
+
+/**
+ * struct uclass - a U-Boot drive class, collecting together similar drivers
+ *
+ * A uclass provides an interface to a particular function, which is
+ * implemented by one or more drivers. Every driver belongs to a uclass even
+ * if it is the only driver in that uclass. An example uclass is GPIO, which
+ * provides the ability to change read inputs, set and clear outputs, etc.
+ * There may be drivers for on-chip SoC GPIO banks, I2C GPIO expanders and
+ * PMIC IO lines, all made available in a unified way through the uclass.
+ *
+ * @priv: Private data for this uclass
+ * @uc_drv: The driver for the uclass itself, not to be confused with a
+ * 'struct driver'
+ * dev_head: List of devices in this uclass (devices are attached to their
+ * uclass when their bind method is called)
+ * @sibling_node: Next uclass in the linked list of uclasses
+ */
+struct uclass {
+	void *priv;
+	struct uclass_driver *uc_drv;
+	struct list_head dev_head;
+	struct list_head sibling_node;
+};
+
+struct device;
+
+/**
+ * struct uclass_driver - Driver for the uclass
+ *
+ * A uclass_driver provides a consistent interface to a set of related
+ * drivers.
+ *
+ * @name: Name of uclass driver
+ * @id: ID number of this uclass
+ * @post_bind: Called after a new device is bound to this uclass
+ * @pre_unbind: Called before a device is unbound from this uclass
+ * @post_probe: Called after a new device is probed
+ * @pre_remove: Called before a device is removed
+ * @init: Called to set up the uclass
+ * @destroy: Called to destroy the uclass
+ * @priv_auto_alloc_size: If non-zero this is the size of the private data
+ * to be allocated in the uclass's ->priv pointer. If zero, then the uclass
+ * driver is responsible for allocating any data required.
+ * @per_device_auto_alloc_size: Each device can hold private data owned
+ * by the uclass. If required this will be automatically allocated if this
+ * value is non-zero.
+ * @ops: Uclass operations, providing the consistent interface to devices
+ * within the uclass.
+ */
+struct uclass_driver {
+	const char *name;
+	enum uclass_id id;
+	int (*post_bind)(struct device *dev);
+	int (*pre_unbind)(struct device *dev);
+	int (*post_probe)(struct device *dev);
+	int (*pre_remove)(struct device *dev);
+	int (*init)(struct uclass *class);
+	int (*destroy)(struct uclass *class);
+	int priv_auto_alloc_size;
+	int per_device_auto_alloc_size;
+	const void *ops;
+};
+
+/* Declare a new uclass_driver */
+#define UCLASS_DRIVER(__name)						\
+	ll_entry_declare(struct uclass_driver, __name, uclass)
+
+/**
+ * uclass_get() - Get a uclass based on an ID, creating it if needed
+ *
+ * Every uclass is identified by an ID, a number from 0 to n-1 where n is
+ * the number of uclasses. This function allows looking up a uclass by its
+ * ID.
+ *
+ * @key: ID to look up
+ * @ucp: Returns pointer to uclass (there is only one per ID)
+ * @return 0 if OK, -ve on error
+ */
+int uclass_get(enum uclass_id key, struct uclass **ucp);
+
+/**
+ * uclass_get_device() - Get a uclass device based on an ID and index
+ *
+ * id: ID to look up
+ * @index: Device number within that uclass (0=first)
+ * @ucp: Returns pointer to uclass (there is only one per for each ID)
+ * @return 0 if OK, -ve on error
+ */
+int uclass_get_device(enum uclass_id id, int index, struct device **ucp);
+
+/**
+ * uclass_first_device() - Get the first device in a uclass
+ *
+ * @id: Uclass ID to look up
+ * @devp: Returns pointer to the first device in that uclass, or NULL if none
+ * @return 0 if OK (found or not found), -1 on error
+ */
+int uclass_first_device(enum uclass_id id, struct device **devp);
+
+/**
+ * uclass_next_device() - Get the next device in a uclass
+ *
+ * @devp: On entry, pointer to device to lookup. On exit, returns pointer
+ * to the next device in the same uclass, or NULL if none
+ * @return 0 if OK (found or not found), -1 on error
+ */
+int uclass_next_device(struct device **devp);
+
+/**
+ * uclass_foreach_dev() - Helper function to iteration through devices
+ *
+ * This creates a for() loop which works through the available devices in
+ * a uclass in order from start to end.
+ *
+ * @pos: struct device * to hold the current device. Set to NULL when there
+ * are no more devices.
+ * uc: uclass to scan
+ */
+#define uclass_foreach_dev(pos, uc)					\
+	for (pos = list_entry((&(uc)->dev_head)->next, typeof(*pos),	\
+			uclass_node);					\
+	     prefetch(pos->uclass_node.next),				\
+			&pos->uclass_node != (&(uc)->dev_head);		\
+	     pos = list_entry(pos->uclass_node.next, typeof(*pos),	\
+			uclass_node))
+
+#endif
diff --git a/include/dm/util.h b/include/dm/util.h
new file mode 100644
index 0000000..8be64a9
--- /dev/null
+++ b/include/dm/util.h
@@ -0,0 +1,29 @@
+/*
+ * Copyright (c) 2013 Google, Inc
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef __DM_UTIL_H
+
+void dm_warn(const char *fmt, ...);
+
+#ifdef DEBUG
+void dm_dbg(const char *fmt, ...);
+#else
+static inline void dm_dbg(const char *fmt, ...)
+{
+}
+#endif
+
+struct list_head;
+
+/**
+ * list_count_items() - Count number of items in a list
+ *
+ * @param head:		Head of list
+ * @return number of items, or 0 if empty
+ */
+int list_count_items(struct list_head *head);
+
+#endif