linux-kernel - Re: [PATCH] 2.6.18-rt7: PowerPC: fix breakage in threaded fasteoi type IRQ handlers

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Message-ID: <4560BA57.40600@ru.mvista.com>
Date:	Sun, 19 Nov 2006 23:11:03 +0300
From:	Sergei Shtylyov <sshtylyov@...mvista.com>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	mingo@...e.hu, linuxppc-dev@...abs.org,
	linux-kernel@...r.kernel.org, dwalker@...sta.com
Subject: Re: [PATCH] 2.6.18-rt7: PowerPC: fix breakage in threaded fasteoi
 type IRQ handlers

Hello.

Benjamin Herrenschmidt wrote:

>>>As fasteoi type chips never had to define their ack() method before the
>>>recent Ingo's change to handle_fasteoi_irq(), any attempt to execute handler
>>>in thread resulted in the kernel crash. So, define their ack() methods to be
>>>the same as their eoi() ones...

>>>Signed-off-by: Sergei Shtylyov <sshtylyov@...mvista.com>

>>>---
>>>Since there was no feedback on three solutions I suggested, I'm going the way
>>>of least resistance and making the fasteoi type chips behave the way that
>>>handle_fasteoi_irq() is expecting from them...

>>Wait wait wait .... Can somebody (Ingo ?) explain me why the fasteoi
>>handler is being changed and what is the rationale for adding an ack
>>that was not necessary before ?

    It's changed in the RT patch for the case of threaded IRQ. This patch is 
not for the mainline kernels.

> To be more precise, I don't see in what circumstances a fasteoi type PIC
> would need an ack routine that does something different than the eoi...
> and if it always does the same thing, why not just call eoi ?

    Because Ingo decided that calling mask() and ack() methods was a better 
than calling mask() and eoi(). Here's the thread:

http://ozlabs.org/pipermail/linuxppc-dev/2006-October/026546.html

> Ben.

WBR, Sergei

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