mirror of
https://github.com/edk2-porting/linux-next.git
synced 2024-12-21 11:44:01 +08:00
d58cb9cc8a
Several drivers use device_create_file() where device.groups should be used instead. This patch documents that and also removes the comments about device classes since these should not be used in new code in the way documented until now in Documentation/driver-model/device.txt. Signed-off-by: Bart Van Assche <bvanassche@acm.org> Cc: Randy Dunlap <rdunlap@xenotime.net> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
107 lines
3.2 KiB
Plaintext
107 lines
3.2 KiB
Plaintext
|
|
The Basic Device Structure
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
See the kerneldoc for the struct device.
|
|
|
|
|
|
Programming Interface
|
|
~~~~~~~~~~~~~~~~~~~~~
|
|
The bus driver that discovers the device uses this to register the
|
|
device with the core:
|
|
|
|
int device_register(struct device * dev);
|
|
|
|
The bus should initialize the following fields:
|
|
|
|
- parent
|
|
- name
|
|
- bus_id
|
|
- bus
|
|
|
|
A device is removed from the core when its reference count goes to
|
|
0. The reference count can be adjusted using:
|
|
|
|
struct device * get_device(struct device * dev);
|
|
void put_device(struct device * dev);
|
|
|
|
get_device() will return a pointer to the struct device passed to it
|
|
if the reference is not already 0 (if it's in the process of being
|
|
removed already).
|
|
|
|
A driver can access the lock in the device structure using:
|
|
|
|
void lock_device(struct device * dev);
|
|
void unlock_device(struct device * dev);
|
|
|
|
|
|
Attributes
|
|
~~~~~~~~~~
|
|
struct device_attribute {
|
|
struct attribute attr;
|
|
ssize_t (*show)(struct device *dev, struct device_attribute *attr,
|
|
char *buf);
|
|
ssize_t (*store)(struct device *dev, struct device_attribute *attr,
|
|
const char *buf, size_t count);
|
|
};
|
|
|
|
Attributes of devices can be exported by a device driver through sysfs.
|
|
|
|
Please see Documentation/filesystems/sysfs.txt for more information
|
|
on how sysfs works.
|
|
|
|
As explained in Documentation/kobject.txt, device attributes must be be
|
|
created before the KOBJ_ADD uevent is generated. The only way to realize
|
|
that is by defining an attribute group.
|
|
|
|
Attributes are declared using a macro called DEVICE_ATTR:
|
|
|
|
#define DEVICE_ATTR(name,mode,show,store)
|
|
|
|
Example:
|
|
|
|
static DEVICE_ATTR(type, 0444, show_type, NULL);
|
|
static DEVICE_ATTR(power, 0644, show_power, store_power);
|
|
|
|
This declares two structures of type struct device_attribute with respective
|
|
names 'dev_attr_type' and 'dev_attr_power'. These two attributes can be
|
|
organized as follows into a group:
|
|
|
|
static struct attribute *dev_attrs[] = {
|
|
&dev_attr_type.attr,
|
|
&dev_attr_power.attr,
|
|
NULL,
|
|
};
|
|
|
|
static struct attribute_group dev_attr_group = {
|
|
.attrs = dev_attrs,
|
|
};
|
|
|
|
static const struct attribute_group *dev_attr_groups[] = {
|
|
&dev_attr_group,
|
|
NULL,
|
|
};
|
|
|
|
This array of groups can then be associated with a device by setting the
|
|
group pointer in struct device before device_register() is invoked:
|
|
|
|
dev->groups = dev_attr_groups;
|
|
device_register(dev);
|
|
|
|
The device_register() function will use the 'groups' pointer to create the
|
|
device attributes and the device_unregister() function will use this pointer
|
|
to remove the device attributes.
|
|
|
|
Word of warning: While the kernel allows device_create_file() and
|
|
device_remove_file() to be called on a device at any time, userspace has
|
|
strict expectations on when attributes get created. When a new device is
|
|
registered in the kernel, a uevent is generated to notify userspace (like
|
|
udev) that a new device is available. If attributes are added after the
|
|
device is registered, then userspace won't get notified and userspace will
|
|
not know about the new attributes.
|
|
|
|
This is important for device driver that need to publish additional
|
|
attributes for a device at driver probe time. If the device driver simply
|
|
calls device_create_file() on the device structure passed to it, then
|
|
userspace will never be notified of the new attributes.
|