From: Eugene Surovegin <ebs@ebshome.net>
To: Tolunay Orkun <listmember@orkun.us>
Cc: linuxppc-embedded@ozlabs.com
Subject: Re: Question regarding Interrupt "delivery" to user mode process
Date: Fri, 25 Mar 2005 10:31:26 -0800 [thread overview]
Message-ID: <20050325183126.GA2539@gate.ebshome.net> (raw)
In-Reply-To: <42444D00.80401@orkun.us>
On Fri, Mar 25, 2005 at 11:40:16AM -0600, Tolunay Orkun wrote:
[snip]
> There is a quirk for PPC405 however: Linux (2.4) calls ack_irq() before
> branching to the IRQ handler. However, if irq is level triggered and
> external interrupt source has not yet deasserted, the interrupt status
> bit in interrupt status register will remain set! To avoid spurious
> interrupt it is necessary to call ack_irq() again before enabling the
> interrupts again. I had discussed this in the old linuxppc-embedded list
> while I was doing this driver.
This isn't 405 specific. This problem will exist on any system with
level-sensitive IRQ source which wasn't ACK'ed. ACK'ed here means
acknowledgment in device itself, not in PIC.
This is why this user-space IRQ handling is a bad idea, IMHO. You have
to ACK IRQ (in device itself) in kernel-IRQ handler.
--
Eugene
next prev parent reply other threads:[~2005-03-25 18:31 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-03-25 16:58 Question regarding Interrupt "delivery" to user mode process Caruso, Nick
2005-03-25 17:40 ` Tolunay Orkun
2005-03-25 18:31 ` Eugene Surovegin [this message]
2005-03-25 19:42 ` Tolunay Orkun
2005-03-25 20:05 ` Tolunay Orkun
2005-03-25 20:37 ` Eugene Surovegin
-- strict thread matches above, loose matches on Subject: below --
2005-03-25 17:19 Stephen Warren
[not found] <20050325221320.004DC67AB2@ozlabs.org>
2005-03-28 16:29 ` David Bruce
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