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Re: [PATCH] Import updates from i386's i8259.c

To: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Subject: Re: [PATCH] Import updates from i386's i8259.c
From: "Maciej W. Rozycki" <macro@linux-mips.org>
Date: Thu, 7 Dec 2006 15:03:48 +0000 (GMT)
Cc: Ralf Baechle <ralf@linux-mips.org>, Atsushi Nemoto <anemo@mba.ocn.ne.jp>, vagabon.xyz@gmail.com, linux-mips@linux-mips.org
In-reply-to: <45781C70.30405@ru.mvista.com>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <20061205194907.GA1088@linux-mips.org> <20061205195702.GA2097@linux-mips.org> <cda58cb80612060040o17ec40f3x4c2f7d0037d3cd1@mail.gmail.com> <20061207.121702.108739943.nemoto@toshiba-tops.co.jp> <20061207115035.GA15386@linux-mips.org> <45781C70.30405@ru.mvista.com>
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On Thu, 7 Dec 2006, Sergei Shtylyov wrote:

>    It's not really related as 8259 is programmed to generate vectors 0x20 to
> 0x2F for x86 but the the IRQs start from zero anyway...

 In Linux most platforms define IRQ numbers in the sense of physical lines 
(or wires if you prefer) routed to inputs of interrupt controllers rather 
than vectors which may or may not be used by a given platform (and to 
complicate things further, the presence of which may be 
software-configurable).  Of course if a message passing concept is used 
for interrupt delivery (be it a simple chain or a more complicated 
protocol), then a different numbering scheme may be required and exposing 
vectors may be a necessity.

 Even with the i8259A there is no need to use its vector at all if the 
processor being interrupted does not issue INTA cycles itself.

  Maciej

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