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    SubjectRe: Git backlight subsystem tree
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    Hi Greg,

    On Thu, 2007-02-08 at 13:23 -0800, Greg KH wrote:
    > On Thu, Feb 08, 2007 at 06:32:02PM +0000, James Simmons wrote:
    > > I CC Greg to explain. The backlight class didn't go away. The way it is
    > > handled is different.
    >
    > Have a pointer to the patch so I can help explain better?

    You've been cc'd on the proposed patch a couple of times in this thread
    so it should be in your mailbox now.

    > As a short summary, 'struct class_device' is going away. Using a
    > 'struct device' in its place is what the conversion should have just
    > done, no functionality change otherwise.

    The backlight class is drivers/video/backlight/backlight.c and if I
    understand things correctly what shows up in sysfs changes.

    At the moment (as I understand the code which could be wrong), the
    backlight functionality is tagged onto an existing device. Taking
    drivers/video/backlight/corgi_bl.c as an example, the corgi_bl device
    exists under /sys/devices/platform/corgi_bl with an associated struct
    device. The backlight code then appends some magic to this to link in
    some class attributes that show up under /sys/class/backlight. There is
    only ever one device.

    By replacing class_device_register() with device_create(), the proposed
    patch appears to generate a second struct device with the original as
    its parent. I'm not sure where it appears in /sys/devices? Having
    another full blown struct device around makes me uneasy as wherever it
    appears, we only have one device, not two.

    If I had some kind of platform device which had an LED, backlight and
    say battery component and registered with the three appropriate classes
    would that mean four struct devices? Where under /sys/devices do they
    each appear?

    Also, it was mentioned that a parent struct device is a requirement and
    this isn't the case for all backlight users. I think this constraint on
    device_create has been removed in more recent code though?

    Richard

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