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SubjectRe: Is it useful to support user level drivers
> > 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.

Unless you need that interrupt to be enabled to deliver the signal or let
userspace reenable the interrupt.

In addition, how do you handle shared interrupts ?

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