linux-kernel - Re: [PATCH] fix return value of i8042_aux_test

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Date:	Thu, 26 Jul 2007 09:54:50 -0400
From:	"Dmitry Torokhov" <dmitry.torokhov@...il.com>
To:	"Fernando Luis Vázquez Cao" 
	<fernando@....ntt.co.jp>
Cc:	linux-kernel@...r.kernel.org, vojtech@...e.cz,
	akpm@...ux-foundation.org
Subject: Re: [PATCH] fix return value of i8042_aux_test_irq

Hi,

On 7/26/07, Fernando Luis Vázquez Cao <fernando@....ntt.co.jp> wrote:
> I made an interesting finding while testing the two patches below.
>
> http://lkml.org/lkml/2007/7/19/685
> http://lkml.org/lkml/2007/7/19/687
>
> These patches modify the traditional CONFIG_DEBUG_KERNEL in such a way
> that the request_irq prints a warning if after calling the handler it
> returned IRQ_HANDLED .
>
> The code looks like this:
>
> int request_irq(unsigned int irq, irq_handler_t handler,
>                unsigned long irqflags, const char *devname, void
> *dev_id)
> .....
>        if (irqflags & IRQF_DISABLED) {
>                unsigned long flags;
>
>                local_irq_save(flags);
>                retval = handler(irq, dev_id);
>                local_irq_restore(flags);
>        } else
>                retval = handler(irq, dev_id);
>        if (retval == IRQ_HANDLED) {
>                printk(KERN_WARNING
>                       "%s (IRQ %d) handled a spurious interrupt\n",
>                       devname, irq);
>        }
> .....
>
> I discovered that i8042_aux_test_irq handles the "fake" interrupt,
> which, in principle, is not correct because it obviously isn't a real
> interrupt and it could have been a spurious interrupt as well.
>
> The problem is that the interrupt handler unconditionally returns IRQ
> handled, which does not seem correct. Anyway I am not very familiar with
> this code so I may be missing the whole point. I would appreciate your
> comments on this.
>

The handler does handle the interrupt - both status and data registers
are read so from the keyboard controller point of view the interrupt
has been handled even if we happen to discard the data. As far as I
know IRQ12 is never shared by BIOS... Vojtech, do you remember why we
request IRQ12 with IRQF_SHARED?

-- 
Dmitry
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