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    SubjectRe: Is it useful to support user level drivers
    On Thu, 21 Jun 2001, Alan Cox wrote:

    > > it would be a good idea to add user level interrupt
    > > support ? I have a framework for it, but it still
    > The problem is that the IRQ has to be cleared in kernel space, because otherwise
    > you may deadlock.

    It depends on device type. Good designed ones does not raises a new
    interrupt until an explicit acknowledge by I/O from [user space] driver
    will be received.

    Access to device's ports and IRQs from user space is subject
    of system admistration policy so direct access to a dangerous devices
    should not be allowed.

    Lastly an IRQ kernel module can disable_irq() from interrupt handler
    and enable it again only on explicit acknowledge from user.

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