linux-kernel - Re: [PATCH] FRV: do_gettimeofday() should no longer use tickadj

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Date:	Thu, 07 Sep 2006 09:01:32 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	David Howells <dhowells@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>, john stultz <johnstul@...ibm.com>,
	Adrian Bunk <bunk@...sta.de>, Andrew Morton <akpm@...l.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	linux-kernel@...r.kernel.org, Jeff Garzik <jeff@...zik.org>,
	netdev@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] FRV: do_gettimeofday() should no longer use tickadj

> Under some circumstances I can work out which sources have triggered which
> interrupts (there are various off-CPU FPGAs which implement auxiliary PICs that
> do announce their sources), but the aux-PIC channels are grouped together upon
> delivery to the CPU PIC, so some of the ACK'ing has to be done at the group
> level.
> 
> > how is this not possible via genirq?
> 
> How is it possible with genirq?

Well, genirq gives you more flexibility than the current mecanism so ...

If I understand correctly, you need to do scray stuff to figure out your
toplevel irq, which shound't be a problem with either mecanisms... 

Now, if you have funky cascades, then you can always group them into a
virtual irq cascade line and have a special chained flow handler that
does all the "figuring out" off those... it's up to you. 

In general, I found genirq allowed me to do more fancy stuff, and end up
with actually less hooks and indirect function calls on the path to a
given irq than before as you can use tailored flow handlers that do just
the right thing.

Ben.

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