linux-kernel - Need help making sense of IRQ API

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Date:	Fri, 29 Jun 2007 15:55:49 -0400
From:	"LOL ER" <cryptococa@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: Need help making sense of IRQ API

Hello,
  I've been trying to make sense of how the kernel (on an i386) calls
__do_IRQ() from do_IRQ() for the past few days to no avail. After
doing some research I found out that do_IRQ() calls the corresponding
"highlevel irq-events handler", this lead me to believe that the
kernel calls __do_IRQ through "desc->handle_irq(irq, desc);" (snippet
from do_IRQ in arch/i386). Looking at the kernel I found a comment
which reads, " * @handle_irq: highlevel irq-events handler [if NULL,
__do_IRQ()]", instinctively I then grepped through the kernel to find
any instances of where handle_IRQ is checked for being NULL. I then
found an inlined function called generic_handle_irq that does just
that. If indeed generic_handle_irq() is the default value of
handle_irq(), why is its datatype not irq_flow_handler_t, and where in
the kernel is it set as the default "highlevel irq-events handler?"
Just to clarify what I mean, the handle_irq member in the irq_desc
struct has its datatype as irq_flow_handler_t, which is a function
pointer that takes 2 arguments,  "unsigned int irq, struct irq_desc
*desc", however unsigned generic_handle_irq() takes one argument,
which is just an int representing the IRQ number.
Thank You,
   Robert G.
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