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Subject[RFC] Some thoughts on device drivers and sysfs
From
Date
One of the original design goals of sysfs was to provide a standardized
location to keep driver configuration attributes. Although sysfs
handles this very well for bus devices and class devices, there isn't
currently a method to export attributes for device drivers and their
specific bound device instances to userspace.

I would like to propose that we create a new type of device that would
act as the layer between physical (bus devices) and logical (class
devices). It could be referred to as a "driver device". Driver devices
would bind to a bus devices and create one or more class devices. Their
type would be of "struct device_driver". As an example, this would
allow us to move something like /proc/driver/emu10k1/0000:01:09.0 into
sysfs.

(physical) | (logical)
------------------------------------------------
|bus device --> driver device --> class device |
------------------------------------------------

struct driver_device {
struct list_head node;
unsigned long id;
struct kobject kobj;
struct device_driver *drv;
struct device *dev;
int state;
};

In sysfs, a new directory could be created to represent driver devices.
It might look like the following:

bus
|
\- pci
|
\- devices
|
\- link to device0
\- link to device1
\- drivers
|
\- link to random_drv (in other words random_drv can drive this bus)

device
|
\- device0
[...]
\- device1
[...]

driver (this directory is new)
|
\- random_drv
|
\- 0 (a sequential instance number) <-- this is a driver device
|
\- link to device0
\- link to class0
\- a file to control driver state (start, stop, etc.)
\- driver attributes for this link
\- 1
|
\- link to device1
\- link to class1
\- a file to control driver state
\- driver attributes for this link

class
|
\-some_type
|
\- class0
[...]
\- class1
[...]

This would allow us to represent per-device driver attributes in sysfs.
As an added benefit, driver devices would allow the tracking and control
of driver state, which may be needed for dynamic power management. I
look forward to any comments.

Thanks,
Adam


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