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