[RFC] Some thoughts on device drivers and sysfs

From: Adam Belay (abelay_at_novell.com)
Date: 03/27/05

  • Next message: Kyle Moffett: "Re: Can't use SYSFS for "Proprietry" driver modules !!!." 
    To: Greg KH <greg@kroah.com>, Patrick Mochel <mochel@digitalimplant.org>
Date:	Sun, 27 Mar 2005 14:24:59 -0500

    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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