DRIVER(9) NetBSD Kernel Manual DRIVER(9)
NAME
driver - description of a device driver
SYNOPSIS
#include <sys/param.h> #include <sys/device.h> #include <sys/error.h> static int foo_match(struct device *parent, struct cfdata *match, void *aux); static void foo_attach(struct device *parent, struct device *self, void *aux); static int foo_detach(struct device *self, int flags); static int foo_activate(struct device *self, enum devact act);
DESCRIPTION
This page briefly describes the basic NetBSD autoconfiguration interface utilised by device drivers. For a detailed overview of the autoconfigu- ration framework see autoconf(9). Each device driver must present to the system a standard autoconfigura- tion interface. This interface is provided by the cfattach structure. The interface to the driver is constant and is defined statically inside the driver. For example, the interface to driver ``foo'' is defined with: struct cfattach foo_ca = { sizeof(struct foo_softc), /* size of instance data */ foo_match, /* match/probe function */ foo_attach, /* attach function */ foo_detach, /* detach function */ foo_activate /* activate function */ }; The structure variable must be named foo_ca by appending the letters ``_ca'' to the driver's base name. This convention is mandated by the autoconfiguration framework. For each device instance controlled by the driver, the autoconfiguration framework allocates a block of memory to record device-instance-specific driver variables. The size of this memory block is specified by the first field in the cfattach structure. The memory block is referred to as the driver's softc structure. The softc structure is only accessed within the driver, so its definition is local to the driver. Neverthe- less, the softc structure should adopt the standard NetBSD configuration and naming conventions. For example, the softc structure for driver ``foo'' is defined with: struct foo_softc { struct device sc_dev; /* generic device info */ /* device-specific state */ }; The autoconfiguration framework mandates that the first member of the softc structure must be the driver-independent struct device. Probably its most useful aspect to the driver is that it contains the device-in- stance name dv_xname. During system bootstrap, the autoconfiguration framework searches the system for devices. For each device driver, its match function is called (via its cfattach structure) to match the driver with a device instance. The match function is called with three arguments. This first argument parent is a pointer to the driver's parent device structure. The second argument match is a pointer to a data structure describing the autocon- figuration framework's understanding of the driver. Both the parent and match arguments are ignored by most drivers. The third argument aux con- tains a pointer to a structure describing a potential device-instance. It is passed to the driver from the parent. The match function would type-cast the aux argument to its appropriate attachment structure and use its contents to determine whether it supports the device. Depending on the device hardware, the contents of the attachment structure may con- tain ``locators'' to locate the device instance so that the driver can probe it for its identity. If the probe process identifies additional device properties, it may modify the members of the attachment structure. For these devices, the NetBSD convention is to call the match routine foo_probe() instead of foo_match() to make this distinction clear. Ei- ther way, the match function returns a nonzero integer indicating the confidence of supporting this device and a value of 0 if the driver doesn't support the device. Generally, only a single driver exists for a device, so the match function returns 1 for a positive match. The autoconfiguration framework will call the attach function (via its cfattach structure) of the driver which returns the highest value from its match function. The attach function is called with three arguments. The attach function performs the necessary process to initialise the de- vice for operation. The first argument parent is a pointer to the driv- er's parent device structure. The second argument self is a pointer to the driver's device structure. It is also a pointer to our softc struc- ture since the device structure is its first member. The third argument aux is a pointer to the attachment structure. The parent and aux argu- ments are the same as passed to the match function. The driver's attach function is called before system interrupts are en- abled. If interrupts are required during initialisation, then the attach function should make use of config_interrupts() (see autoconf(9)). Some devices can be removed from the system without requiring a system reboot. The autoconfiguration framework calls the driver's detach func- tion (via its cfattach structure) during device detachment. If the de- vice does not support detachment, then the driver does not have to pro- vide a detach function. The detach function is used to relinquish re- sources allocated to the driver which are no longer needed. The first argument self is a pointer to the driver's device structure. It is the same structure as passed to the attach function. The second argument flags contains detachment flags. Valid values are DETACH_FORCE (force detachment; hardware gone) and DETACH_QUIET (do not print a notice). The autoconfiguration framework calls the driver's activate function to notify the driver of a change in the resources that have been allocated to it. For example, an Ethernet driver has to be notified if the network stack is being added or removed from the kernel. The first argument to the activate function self is a pointer to the driver's device structure. It is the same argument as passed to the attach function. The second ar- gument act describes the action. Valid actions are DVACT_ACTIVATE (activate the device) and DVACT_DEACTIVATE (deactivate the device). If the action is not supported the activate function should return EOPNO- SUPP. The activate function is called in interrupt context. Most drivers will want to make use of interrupt facilities. Interrupt locators provided through the attachment structure should be used to es- tablish interrupts within the system. Generally, an interrupt interface is provided by the parent. The interface will require a handler and a driver-specific argument to be specified. This argument is usually a pointer to the device-instance-specific softc structure. When a hardware interrupt for the device occurs the handler is called with the argument. Interrupt handlers should return 0 for ``interrupt not for me'', 1 for ``I took care of it'', or -1 for ``I guess it was mine, but I wasn't expecting it''. For a driver to be compiled into the kernel, config(8) must be aware of its existence. This is done by including an entry in files.<bus> in the directory containing the driver. For example, the driver ``foo'' attach- ing to bus ``bar'' with dependency on kernel module ``baz'' has the en- try: device foo: baz attach foo at bar file dev/bar/foo.c foo An entry can now be added to the machine description file: foo* at bar? For a detailed description of the machine description file and the ``device definition'' language see config(9).
SEE ALSO
config(8), autoconf(9), config(9), powerhook_establish(9), shutdownhook_establish(9) NetBSD 1.6 June 16, 2001 3
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