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

> > Lastly an IRQ kernel module can disable_irq() from interrupt handler
> > and enable it again only on explicit acknowledge from user.
>
> No. The IRQ might be shared, and you get a slight problem if you just disabled
> an IRQ needed to make progress for user space to handle the IRQ

Disabling the IRQ till user acknowledge is an option for particular
device handling.
Yes, IRQ sharing is impossible with it and IRQ module must reject setup
requests with this option and SA_SHIRQ flag together.
However, it is important for rare cases only with "bad" devices
(their interrupt behaviour is really bad!) and IRQ sharing requirement.

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