linux-kernel - Re: [Patch/RFC]: check CONFIG_GENERIC_HARDIRQS for request/free

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Message-Id: <200805301336.03317.rusty@rustcorp.com.au>
Date:	Fri, 30 May 2008 13:36:02 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Christian Borntraeger <borntraeger@...ibm.com>
Cc:	schwidefsky@...ibm.com, LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	will schmidt <will_schmidt@...t.ibm.com>
Subject: Re: [Patch/RFC]: check CONFIG_GENERIC_HARDIRQS for request/free_irq in interrupt.h

On Friday 30 May 2008 04:32:58 Christian Borntraeger wrote:
> Am Donnerstag, 29. Mai 2008 schrieb Martin Schwidefsky:
> > On Thu, 2008-05-29 at 17:41 +0200, Christian Borntraeger wrote:
> > > I currently try to evaluate virtio_console for kvm on s390 and got
> > > the following problem:
> > >
> > > virtio_console uses hvc_alloc with irq=0. That means, register_irq
> > > and free_irq are never called by hvc_console.c, but the linker will
> > > still complain about unknown references to free_irq and request_irq.
> > >
> > > As the whole kernel/irq folder depends on CONFIG_GENERIC_HARDIRQS
> > > it seems consistent to declare all functions from kernel/irq only if
> > > CONFIG_GENERIC_HARDIRQS is set. Otherwise we can use empty functions.
> > >
> > > This patch does that for register_irq and free_irq.
> > >
> > > Comments?
> >
> > Please don't. So far whenever the linker complained about the missing
> > register_irq/free_irq functions it has been a bug in a Kconfig file.
> > We should not silently accept code that requires the concept of an
> > irq-line when there is no such thing on a s390.
>
> Ok, convinced.
>
> I will look if I can modify virtio_console to get rid of hvc_console.
> Reading all the comments, it appears that Rusty is not really happy with
> all the dependencies/limitations that hvc_console brings to virtio_console.
>
> Rusty, be prepared.... ;-)
>
> Christian

OK, my plan was to at least allow the hook of notifiers in hvc_console, rather 
than relying on interrupts or nothing.  Then expose "use interrupt to notify" 
and "use a backoff timer to notify" helpers and let the caller hook one up.

But it was a vague plan which may become unrecognisable when meeting 
reality...

Cheers,
Rusty.




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