new file mode 100644
@@ -0,0 +1,43 @@
+==================
+Device connections
+==================
+
+Introduction
+------------
+
+Devices have often connections to other devices that are out side of the direct
+child/parent relationship. A serial or network communication controller, which
+could be a PCI device, may need to be able to get a reference to its PHY
+component, which could be attached to for example the I2C bus. Some device
+drivers need to be able to control the clocks or the GPIOs for their devices,
+and so on.
+
+Device connections are generic descriptions of any type of connection between
+two separate devices.
+
+Device connections alone do not create a dependency between the two devices.
+They are only descriptions which are not tied to either of devices directly.
+A dependency between the two devices exists only if one of the two endpoint
+devices requests a reference to the other. The descriptions themselves can be
+defined in firmware (not yet supported) or they can be build-in.
+
+Usage
+-----
+
+Device connections should exist before device ``->probe`` callback is called for
+either endpoint devices in the description. If the connections are defined in
+firmware, this is not a problem. It should be considered if the connection
+descriptions are "build-in", and need to be added separately.
+
+The connection description consist of the names of the two devices with the
+connection, i.e. the endpoints, and unique identifier for the connection which
+is needed if there are multiple connections between the two devices.
+
+After a descriptions exist, the devices in it can request reference to the other
+endpoint device, or they can request the description itself.
+
+API
+---
+
+.. kernel-doc:: drivers/base/devcon.c
+ : functions: __device_find_connection device_find_connection add_device_connection remove_device_connection
@@ -5,7 +5,8 @@ obj-y := component.o core.o bus.o dd.o syscore.o \
driver.o class.o platform.o \
cpu.o firmware.o init.o map.o devres.o \
attribute_container.o transport_class.o \
- topology.o container.o property.o cacheinfo.o
+ topology.o container.o property.o cacheinfo.o \
+ devcon.o
obj-$(CONFIG_DEVTMPFS) += devtmpfs.o
obj-$(CONFIG_DMA_CMA) += dma-contiguous.o
obj-y += power/
new file mode 100644
@@ -0,0 +1,139 @@
+// SPDX-License-Identifier: GPL-2.0
+/**
+ * Device connections
+ *
+ * Copyright (C) 2018 Intel Corporation
+ * Author: Heikki Krogerus <heikki.krogerus@linux.intel.com>
+ */
+
+#include <linux/connection.h>
+#include <linux/device.h>
+
+static DEFINE_MUTEX(devcon_lock);
+static LIST_HEAD(devcon_list);
+
+/**
+ * __device_find_connection - Find physical connection to a device
+ * @dev: Device with the connection
+ * @con_id: Identifier for the connection
+ * @data: Data for the match function
+ * @match: Function to check and convert the connection description
+ *
+ * Find a connection with unique identifier @con_id between @dev and an other
+ * device. @match will be used to convert the connection description to data the
+ * caller is expecting to be returned.
+ */
+void *__device_find_connection(struct device *dev, const char *con_id,
+ void *data,
+ void *(*match)(struct devcon *con, int ep,
+ void *data))
+{
+ const char *devname = dev_name(dev);
+ struct devcon *con;
+ void *ret = NULL;
+ int ep;
+
+ if (!match)
+ return NULL;
+
+ rcu_read_lock();
+
+ list_for_each_entry_rcu(con, &devcon_list, list) {
+ ep = match_string(con->endpoint, 2, devname);
+ if (ep < 0)
+ continue;
+
+ if (con_id && strcmp(con->id, con_id))
+ continue;
+
+ ret = match(con, !ep, data);
+ if (ret)
+ break;
+ }
+
+ rcu_read_unlock();
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(__device_find_connection);
+
+#include <linux/platform_device.h>
+#include <linux/spi/spi.h>
+#include <linux/i2c.h>
+#include <linux/pci.h>
+
+static struct bus_type *generic_match_buses[] = {
+ &platform_bus_type,
+#ifdef CONFIG_PCI
+ &pci_bus_type,
+#endif
+#ifdef CONFIG_I2C
+ &i2c_bus_type,
+#endif
+#ifdef CONFIG_SPI_MASTER
+ &spi_bus_type,
+#endif
+ NULL,
+};
+
+/* This tries to find the device from the most common bus types by name. */
+static void *generic_match(struct devcon *con, int ep, void *data)
+{
+ struct bus_type *bus;
+ struct device *dev;
+
+ for (bus = generic_match_buses[0]; bus; bus++) {
+ dev = bus_find_device_by_name(bus, NULL, con->endpoint[ep]);
+ if (dev)
+ return dev;
+ }
+
+ /*
+ * We only get called if a connection was found, tell the caller to
+ * wait for the other device to show-up.
+ */
+ return ERR_PTR(-EPROBE_DEFER);
+}
+
+/**
+ * device_find_connection - Find two devices connected together
+ * @dev: Device with the connection
+ * @con_id: Identifier for the connection
+ *
+ * Find a connection with unique identifier @con_id between @dev and an
+ * other device. On success returns handle to the device that is connected
+ * to @dev, with the reference count for the found device incremented. Returns
+ * NULL if no matching connection was found, or ERR_PTR(-EPROBE_DEFER) when a
+ * connection was found but the other device has not been enumerated yet.
+ */
+struct device *device_find_connection(struct device *dev, const char *con_id)
+{
+ return __device_find_connection(dev, con_id, generic_match, NULL);
+}
+EXPORT_SYMBOL_GPL(device_find_connection);
+
+/**
+ * add_device_connection - Register a collection of connection descriptions
+ * @con: Collection of connection descriptions to be registered
+ */
+void add_device_connection(struct devcon *con)
+{
+ mutex_lock(&devcon_lock);
+ list_add_tail_rcu(&con->list, &devcon_list);
+ mutex_unlock(&devcon_lock);
+}
+EXPORT_SYMBOL_GPL(add_device_connection);
+
+/**
+ * remove_device_connections - Unregister collection of connection descriptions
+ * @con: Collection of connection descriptions to be unregistered
+ */
+void remove_device_connection(struct devcon *con)
+{
+ mutex_lock(&devcon_lock);
+ list_del_rcu(&con->list);
+ mutex_unlock(&devcon_lock);
+ /* The caller may free the devcon struct immediately afterwards. */
+ synchronize_rcu();
+}
+EXPORT_SYMBOL_GPL(remove_device_connection);
new file mode 100644
@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#ifndef _LINUX_CONNECTION_H_
+#define _LINUX_CONNECTION_H_
+
+#include <linux/list.h>
+
+struct device;
+
+/**
+ * struct devcon - Device Connection Descriptor
+ * @endpoint: The names of the two devices connected together
+ * @id: Unique identifier for the connection
+ */
+struct devcon {
+ const char *endpoint[2];
+ const char *id;
+ struct list_head list;
+};
+
+void *__device_find_connection(struct device *dev, const char *con_id,
+ void *data,
+ void *(*match)(struct devcon *con, int ep,
+ void *data));
+
+struct device *device_find_connection(struct device *dev, const char *con_id);
+
+#define DEVCON(_ep0, _ep1, _id) { { _ep0, _ep1 }, _id, }
+
+void add_device_connection(struct devcon *con);
+void remove_device_connection(struct devcon *con);
+
+#endif /* _LINUX_CONNECTION_H_ */