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Re: about cs5536 interrupt ack

To: Songmao Tian <tiansm@lemote.com>
Subject: Re: about cs5536 interrupt ack
From: "Maciej W. Rozycki" <macro@linux-mips.org>
Date: Mon, 16 Jul 2007 16:11:45 +0100 (BST)
Cc: LinuxBIOS Mailing List <linuxbios@linuxbios.org>, marc.jones@amd.com, linux-kernel@vger.kernel.org, linux-mips@linux-mips.org
In-reply-to: <4695D78F.8010806@lemote.com>
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References: <4694A495.1050006@lemote.com> <Pine.LNX.4.64N.0707111347360.26459@blysk.ds.pg.gda.pl> <4694F4EB.8040000@lemote.com> <Pine.LNX.4.64N.0707111634430.26459@blysk.ds.pg.gda.pl> <4695D78F.8010806@lemote.com>
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On Thu, 12 Jul 2007, Songmao Tian wrote:

> 8259 problem  seems to be done with the attached patch, IDE hung seems to be
> the dma setting problem.
> 
> Thanks all for your advise, comments. I have learned a lot. now I continue to
> trace down the IDE problem.

 I would still recommend you to investigate the option of making the 8259A 
cores "transparent" and using the mapper registers to dispatch interrupts 
directly -- it would make processing of interrupt requests considerably 
faster and less complicated.  Please note that ffs() is O(1) and actually 
some two or three machine instructions on MIPS architecture processors and 
the model used by the mapper is closer to the spirit of how MIPS 
processors do interrupt handling.  With such an approach it will also 
likely be easier to integrate your changes upstream, than it would for 
your changes to i8259.{c,h} needed for your unusual setup to work.

 Of course as an intermediate solution during development to make the 
whole thing work the complicated use of the 8259A cores may be justified.

  Maciej

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