ACPI / scan: Introduce struct acpi_scan_handler

Introduce struct acpi_scan_handler for representing objects that
will do configuration tasks depending on ACPI device nodes'
hardware IDs (HIDs).

Currently, those tasks are done either directly by the ACPI namespace
scanning code or by ACPI device drivers designed specifically for
this purpose.  None of the above is desirable, however, because
doing that directly in the namespace scanning code makes that code
overly complicated and difficult to follow and doing that in
"special" device drivers leads to a great deal of confusion about
their role and to confusing interactions with the driver core (for
example, sysfs directories are created for those drivers, but they
are completely unnecessary and only increase the kernel's memory
footprint in vain).

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Yinghai Lu <yinghai@kernel.org>
Acked-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Acked-by: Toshi Kani <toshi.kani@hp.com>

Documentation/acpi/scan_handlers.txt

@@ -0,0 +1,77 @@
+ACPI Scan Handlers
+
+Copyright (C) 2012, Intel Corporation
+Author: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
+
+During system initialization and ACPI-based device hot-add, the ACPI namespace
+is scanned in search of device objects that generally represent various pieces
+of hardware.  This causes a struct acpi_device object to be created and
+registered with the driver core for every device object in the ACPI namespace
+and the hierarchy of those struct acpi_device objects reflects the namespace
+layout (i.e. parent device objects in the namespace are represented by parent
+struct acpi_device objects and analogously for their children).  Those struct
+acpi_device objects are referred to as "device nodes" in what follows, but they
+should not be confused with struct device_node objects used by the Device Trees
+parsing code (although their role is analogous to the role of those objects).
+
+During ACPI-based device hot-remove device nodes representing pieces of hardware
+being removed are unregistered and deleted.
+
+The core ACPI namespace scanning code in drivers/acpi/scan.c carries out basic
+initialization of device nodes, such as retrieving common configuration
+information from the device objects represented by them and populating them with
+appropriate data, but some of them require additional handling after they have
+been registered.  For example, if the given device node represents a PCI host
+bridge, its registration should cause the PCI bus under that bridge to be
+enumerated and PCI devices on that bus to be registered with the driver core.
+Similarly, if the device node represents a PCI interrupt link, it is necessary
+to configure that link so that the kernel can use it.
+
+Those additional configuration tasks usually depend on the type of the hardware
+component represented by the given device node which can be determined on the
+basis of the device node's hardware ID (HID).  They are performed by objects
+called ACPI scan handlers represented by the following structure:
+
+struct acpi_scan_handler {
+	const struct acpi_device_id *ids;
+	struct list_head list_node;
+	int (*attach)(struct acpi_device *dev, const struct acpi_device_id *id);
+	void (*detach)(struct acpi_device *dev);
+};
+
+where ids is the list of IDs of device nodes the given handler is supposed to
+take care of, list_node is the hook to the global list of ACPI scan handlers
+maintained by the ACPI core and the .attach() and .detach() callbacks are
+executed, respectively, after registration of new device nodes and before
+unregistration of device nodes the handler attached to previously.
+
+The namespace scanning function, acpi_bus_scan(), first registers all of the
+device nodes in the given namespace scope with the driver core.  Then, it tries
+to match a scan handler against each of them using the ids arrays of the
+available scan handlers.  If a matching scan handler is found, its .attach()
+callback is executed for the given device node.  If that callback returns 1,
+that means that the handler has claimed the device node and is now responsible
+for carrying out any additional configuration tasks related to it.  It also will
+be responsible for preparing the device node for unregistration in that case.
+The device node's handler field is then populated with the address of the scan
+handler that has claimed it.
+
+If the .attach() callback returns 0, it means that the device node is not
+interesting to the given scan handler and may be matched against the next scan
+handler in the list.  If it returns a (negative) error code, that means that
+the namespace scan should be terminated due to a serious error.  The error code
+returned should then reflect the type of the error.
+
+The namespace trimming function, acpi_bus_trim(), first executes .detach()
+callbacks from the scan handlers of all device nodes in the given namespace
+scope (if they have scan handlers).  Next, it unregisters all of the device
+nodes in that scope.
+
+ACPI scan handlers can be added to the list maintained by the ACPI core with the
+help of the acpi_scan_add_handler() function taking a pointer to the new scan
+handler as an argument.  The order in which scan handlers are added to the list
+is the order in which they are matched against device nodes during namespace
+scans.
+
+All scan handles must be added to the list before acpi_bus_scan() is run for the
+first time and they cannot be removed from it.

drivers/acpi/scan.c

@@ -53,6 +53,7 @@ static const struct acpi_device_id acpi_platform_device_ids[] = {
 static LIST_HEAD(acpi_device_list);
 static LIST_HEAD(acpi_bus_id_list);
 static DEFINE_MUTEX(acpi_scan_lock);
+static LIST_HEAD(acpi_scan_handlers_list);
 DEFINE_MUTEX(acpi_device_lock);
 LIST_HEAD(acpi_wakeup_device_list);
 
@@ -62,6 +63,15 @@ struct acpi_device_bus_id{
 	struct list_head node;
 };
 
+int acpi_scan_add_handler(struct acpi_scan_handler *handler)
+{
+	if (!handler || !handler->attach)
+		return -EINVAL;
+
+	list_add_tail(&handler->list_node, &acpi_scan_handlers_list);
+	return 0;
+}
+
 /*
  * Creates hid/cid(s) string needed for modalias and uevent
  * e.g. on a device with hid:IBM0001 and cid:ACPI0001 you get:
@@ -1570,20 +1580,42 @@ static acpi_status acpi_bus_check_add(acpi_handle handle, u32 lvl_not_used,
 	return AE_OK;
 }
 
+static int acpi_scan_attach_handler(struct acpi_device *device)
+{
+	struct acpi_scan_handler *handler;
+	int ret = 0;
+
+	list_for_each_entry(handler, &acpi_scan_handlers_list, list_node) {
+		const struct acpi_device_id *id;
+
+		id = __acpi_match_device(device, handler->ids);
+		if (!id)
+			continue;
+
+		ret = handler->attach(device, id);
+		if (ret > 0) {
+			device->handler = handler;
+			break;
+		} else if (ret < 0) {
+			break;
+		}
+	}
+	return ret;
+}
+
 static acpi_status acpi_bus_device_attach(acpi_handle handle, u32 lvl_not_used,
 					  void *not_used, void **ret_not_used)
 {
 	const struct acpi_device_id *id;
-	acpi_status status = AE_OK;
 	struct acpi_device *device;
 	unsigned long long sta_not_used;
-	int type_not_used;
+	int ret;
 
 	/*
 	 * Ignore errors ignored by acpi_bus_check_add() to avoid terminating
 	 * namespace walks prematurely.
 	 */
-	if (acpi_bus_type_and_status(handle, &type_not_used, &sta_not_used))
+	if (acpi_bus_type_and_status(handle, &ret, &sta_not_used))
 		return AE_OK;
 
 	if (acpi_bus_get_device(handle, &device))
@@ -1593,10 +1625,15 @@ static acpi_status acpi_bus_device_attach(acpi_handle handle, u32 lvl_not_used,
 	if (id) {
 		/* This is a known good platform device. */
 		acpi_create_platform_device(device, id->driver_data);
-	} else if (device_attach(&device->dev) < 0) {
-		status = AE_CTRL_DEPTH;
+		return AE_OK;
 	}
-	return status;
+
+	ret = acpi_scan_attach_handler(device);
+	if (ret)
+		return ret > 0 ? AE_OK : AE_CTRL_DEPTH;
+
+	ret = device_attach(&device->dev);
+	return ret >= 0 ? AE_OK : AE_CTRL_DEPTH;
 }
 
 /**
@@ -1639,8 +1676,17 @@ static acpi_status acpi_bus_device_detach(acpi_handle handle, u32 lvl_not_used,
 	struct acpi_device *device = NULL;
 
 	if (!acpi_bus_get_device(handle, &device)) {
+		struct acpi_scan_handler *dev_handler = device->handler;
+
 		device->removal_type = ACPI_BUS_REMOVAL_EJECT;
-		device_release_driver(&device->dev);
+		if (dev_handler) {
+			if (dev_handler->detach)
+				dev_handler->detach(device);
+
+			device->handler = NULL;
+		} else {
+			device_release_driver(&device->dev);
+		}
 	}
 	return AE_OK;
 }

include/acpi/acpi_bus.h

@@ -83,6 +83,18 @@ enum acpi_bus_device_type {
 struct acpi_driver;
 struct acpi_device;
 
+/*
+ * ACPI Scan Handler
+ * -----------------
+ */
+
+struct acpi_scan_handler {
+	const struct acpi_device_id *ids;
+	struct list_head list_node;
+	int (*attach)(struct acpi_device *dev, const struct acpi_device_id *id);
+	void (*detach)(struct acpi_device *dev);
+};
+
 /*
  * ACPI Driver
  * -----------
@@ -269,6 +281,7 @@ struct acpi_device {
 	struct acpi_device_wakeup wakeup;
 	struct acpi_device_perf performance;
 	struct acpi_device_dir dir;
+	struct acpi_scan_handler *handler;
 	struct acpi_driver *driver;
 	void *driver_data;
 	struct device dev;
@@ -382,6 +395,7 @@ int acpi_bus_receive_event(struct acpi_bus_event *event);
 static inline int acpi_bus_generate_proc_event(struct acpi_device *device, u8 type, int data)
 	{ return 0; }
 #endif
+int acpi_scan_add_handler(struct acpi_scan_handler *handler);
 int acpi_bus_register_driver(struct acpi_driver *driver);
 void acpi_bus_unregister_driver(struct acpi_driver *driver);
 int acpi_bus_scan(acpi_handle handle);