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diff --git a/Documentation/driver-api/acpi/scan_handlers.rst b/Documentation/driver-api/acpi/scan_handlers.rst new file mode 100644 index 000000000..7a197b3a3 --- /dev/null +++ b/Documentation/driver-api/acpi/scan_handlers.rst @@ -0,0 +1,83 @@ +.. SPDX-License-Identifier: GPL-2.0 +.. include:: <isonum.txt> + +================== +ACPI Scan Handlers +================== + +:Copyright: |copy| 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. |