Get rid of IRQF_DISABLED - (was [PATCH] genirq: warn about IRQF_SHARED|IRQF_DISABLED)

[Russell King - ARM Linux]

On Mon, Nov 30, 2009 at 02:47:02PM +0000, Alan Cox wrote:
> SHARED|DISABLED ought to WARN_ON() and if that doesn't motivate people
> then return -EINVAL.

That is an impossibility.  There is hardware out there (AT91) where
the timer interrupt is shared with other peripherals, and you end
up with a mixture of irqs-disabled and irqs-enabled handlers sharing
the same interrupt.

Luckily, the timer interrupt is the first to claim, and so is the first
to be run.  However, there was a problem reported a while back of the
clock event code being called on AT91 with IRQs enabled - unfortunately
the original reporters stopped responding so it was never worked out
what was going on.

My point is that if we outlaw irqs-disabled shared interrupts, it puts
Atmel AT91 support into immediate difficulties.