From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Thu, 26 Jul 2007 16:04:42 -0700 (PDT)

quoted text
> Quite frankly, my preference would be (a) followed by (e) or (f), and 
> (b)-(d) are in my opinion the worst of the lot with no upsides at all (and 
> (b) in particular is pretty much _guaranteed_ to break existing setups).

I look at some cases, such as EHEA on powerpc which is a pretty
modern driver written by not clueless folks, and wonder if they
do it because they know the IRQ is non-shared, they know their
interrupt handler is insanely simple and short, and just want to
avoid the overhead of that sti()/cli() in the caller.

All the EHEA interrupt handler does is unconditionally set a state bit
and schedule a softirq, then return.

The powerpc folks do delayed IRQ enable/disable using software state,
but perhaps these drivers were written before that.
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