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    SubjectRe: [PATCH] Dell laptop backlight driver
    Matt Domsch wrote:
    > On Sun, Oct 28, 2007 at 05:12:37PM +0100, jack@antonello.org wrote:
    >> Hello,
    >> this driver implements backlight control on Dell laptops
    >> which use SMI for changing brightness levels.
    >>
    >> The driver is INCOMPLETE since it is unable to probe some required
    >> parameters
    >> in order to perform backlight control. Such parameters are found in a Dell
    >> proprietary DMI table which should be parsed. For now external tools may be
    >> used to find these parameters by hand. So if you intend to try this out,
    >> FIRST write your laptop model parameters correctly inside the source code
    >> as explained in Documentation/dell-laptop.txt.
    >>
    >> Parts of this driver may also be used to provide additional functionalities
    >> similarly to the drivers/misc/*-laptop.c drivers.
    >
    > Why is this better done in the kernel rather than in userspace with
    > libsmbios as you've noted?
    >

    I had to do a kernelspace driver for controlling the backlight. This
    was part of a college project assignment. In order for it to be valid
    for an operating system course, it had to be in kernelspace (not
    Unix programming) :).

    As i mentioned that can be done in userspace and it IS sensible to do
    so. I know that the code which was already written for Dell implied
    a userspace approach, but i simply had no choice.

    I also don't expect this driver to become mainstream, but since i have
    written it, other people might want to have a look at it.

    Finally i really don't think there's any sensible way of implementing
    Linux LCD Backlight Abstraction relying on a userspace application.
    That would mean the kernel calling userspace code to change the
    brightness, then this latter code would again call the kernel to trigger
    a SMI and so on. That's just not a good design. I think a userspace
    solution implies choosing NOT to implement the LCD Abstraction. Causing
    Dell laptops to be treated differently from other machines (as they are
    not compliant with Linux's own interface).

    jacopo

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