Based on kernel version 4.16.1. Page generated on 2018-04-09 11:52 EST.
1 ACPI Scan Handlers 2 3 Copyright (C) 2012, Intel Corporation 4 Author: Rafael J. Wysocki <rafael.j.wysocki@intel.com> 5 6 During system initialization and ACPI-based device hot-add, the ACPI namespace 7 is scanned in search of device objects that generally represent various pieces 8 of hardware. This causes a struct acpi_device object to be created and 9 registered with the driver core for every device object in the ACPI namespace 10 and the hierarchy of those struct acpi_device objects reflects the namespace 11 layout (i.e. parent device objects in the namespace are represented by parent 12 struct acpi_device objects and analogously for their children). Those struct 13 acpi_device objects are referred to as "device nodes" in what follows, but they 14 should not be confused with struct device_node objects used by the Device Trees 15 parsing code (although their role is analogous to the role of those objects). 16 17 During ACPI-based device hot-remove device nodes representing pieces of hardware 18 being removed are unregistered and deleted. 19 20 The core ACPI namespace scanning code in drivers/acpi/scan.c carries out basic 21 initialization of device nodes, such as retrieving common configuration 22 information from the device objects represented by them and populating them with 23 appropriate data, but some of them require additional handling after they have 24 been registered. For example, if the given device node represents a PCI host 25 bridge, its registration should cause the PCI bus under that bridge to be 26 enumerated and PCI devices on that bus to be registered with the driver core. 27 Similarly, if the device node represents a PCI interrupt link, it is necessary 28 to configure that link so that the kernel can use it. 29 30 Those additional configuration tasks usually depend on the type of the hardware 31 component represented by the given device node which can be determined on the 32 basis of the device node's hardware ID (HID). They are performed by objects 33 called ACPI scan handlers represented by the following structure: 34 35 struct acpi_scan_handler { 36 const struct acpi_device_id *ids; 37 struct list_head list_node; 38 int (*attach)(struct acpi_device *dev, const struct acpi_device_id *id); 39 void (*detach)(struct acpi_device *dev); 40 }; 41 42 where ids is the list of IDs of device nodes the given handler is supposed to 43 take care of, list_node is the hook to the global list of ACPI scan handlers 44 maintained by the ACPI core and the .attach() and .detach() callbacks are 45 executed, respectively, after registration of new device nodes and before 46 unregistration of device nodes the handler attached to previously. 47 48 The namespace scanning function, acpi_bus_scan(), first registers all of the 49 device nodes in the given namespace scope with the driver core. Then, it tries 50 to match a scan handler against each of them using the ids arrays of the 51 available scan handlers. If a matching scan handler is found, its .attach() 52 callback is executed for the given device node. If that callback returns 1, 53 that means that the handler has claimed the device node and is now responsible 54 for carrying out any additional configuration tasks related to it. It also will 55 be responsible for preparing the device node for unregistration in that case. 56 The device node's handler field is then populated with the address of the scan 57 handler that has claimed it. 58 59 If the .attach() callback returns 0, it means that the device node is not 60 interesting to the given scan handler and may be matched against the next scan 61 handler in the list. If it returns a (negative) error code, that means that 62 the namespace scan should be terminated due to a serious error. The error code 63 returned should then reflect the type of the error. 64 65 The namespace trimming function, acpi_bus_trim(), first executes .detach() 66 callbacks from the scan handlers of all device nodes in the given namespace 67 scope (if they have scan handlers). Next, it unregisters all of the device 68 nodes in that scope. 69 70 ACPI scan handlers can be added to the list maintained by the ACPI core with the 71 help of the acpi_scan_add_handler() function taking a pointer to the new scan 72 handler as an argument. The order in which scan handlers are added to the list 73 is the order in which they are matched against device nodes during namespace 74 scans. 75 76 All scan handles must be added to the list before acpi_bus_scan() is run for the 77 first time and they cannot be removed from it.