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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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