linux-kernel - Re: [RT] MPIC edge sensitive issues with hardirq preemption

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Date:	Tue, 1 Jul 2008 15:34:53 +0400
From:	Anton Vorontsov <avorontsov@...mvista.com>
To:	Sergei Shtylyov <sshtylyov@...mvista.com>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Ingo Molnar <mingo@...e.hu>,
	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Daniel Walker <dwalker@...sta.com>
Subject: Re: [RT] MPIC edge sensitive issues with hardirq preemption

On Tue, Jul 01, 2008 at 02:41:19PM +0400, Sergei Shtylyov wrote:
> Hello.
>
> Anton Vorontsov wrote:
>
>> But how this could be a bug in the PIC code? IMO this is a bug in the
>> kernel/irq code, since it assumes that fasteoi PIC will retrigger masked
>> edge sources... This isn't true for at least MPIC. To make this work for
>> all fasteoi PICs, we should mask edge sensitive interrupts very very
>> carefully.
>>   
>
>   I guess it assumed this based on 8259's behavior (not sure about I/O  
> APIC).
>   Hm, but the 8259 code never used "fasteoi" path for some obscure  
> reason...
>
>> jammed with the idea that MPIC irq type 0 is low level sensitive, but the
>> true thing is that it is rising edge sensitive. (Ah, I know where I got
>> confused, type 0 is active-low for ISA PICs).
>>   
>
>    You mean in the device tree?

Yes, simply changing device tree.

>> So in all my previous emails I was wrong when I was saying "mpic is
>> programmed to low level sensitive". It was programmed for rising edge
>> sensitive. An all my further reasonings were flawed because of this.
>>   
>
>   Gah.  I'm surprised how it could work at all then...
>
>> Re-programming MPIC to high level sensitive also makes IDE work. But
>> this doesn't mean that IRQ code is correct.
>>   
>
>   I wonder why. :-O
>   Your ULi IDE is in native mode, so it should be generating a PCI  
> interrupt -- which is *low* level sensitive.

Exactly. This is another reason why I was so confused.

-- 
Anton Vorontsov
email: cbouatmailru@...il.com
irc://irc.freenode.net/bd2
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