From mboxrd@z Thu Jan  1 00:00:00 1970
From: benoar@dolka.fr (Benjamin Cama)
Date: Fri, 19 Jun 2015 03:38:15 +0200
Subject: [PATCH] Re: Linkstation Mini and __machine_arch_type problem,
 not booting since 3.8
In-Reply-To: <558278A8.2050406@arm.com>
References: <97db3502cd014faf1c710b1cc0fe8848@dolka.fr>
 <1434446447.4785.7.camel@dolka.fr> <1434593555.13334.14.camel@dolka.fr>
 <558278A8.2050406@arm.com>
Message-ID: <1434677895.4767.11.camel@dolka.fr>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

Hi Marc,

Le jeudi 18 juin 2015 ? 08:52 +0100, Marc Zyngier a ?crit :
> On 18/06/15 03:12, Benjamin Cama wrote:
> > And I did it. And I stumbled upon commit
> > a71b092a9c68685a270ebdde7b5986ba8787e575 ?ARM: Convert handle_IRQ to
> > use __handle_domain_irq? (author Cc'ed). The new function
> > __handle_domain_irq (in kernel/irq/irqdesc.c, which comes just two
> > commits before, with 76ba59f8366f2d9282cb5bda9de75b4b68cbe55f) is
> > subtly different from the one it replaces, handle_IRQ, as it checks if
> > the irq is not 0 as well as checking for an upper bound. Removing the
> > check for 0 makes my machine work again! But honestly, I do not know if
> > a zero irq is legit, so I hope some more knowledgeable people will tell
> > me if this is OK.
> > 
> > -- >8 --
> > Subject: [PATCH] Make __handle_domain_irq accept IRQ 0
> > 
> > The same as handle_IRQ did before.
> > 
> > Signed-off-by: Benjamin Cama <benoar@dolka.fr>
> > ---
> >  kernel/irq/irqdesc.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/kernel/irq/irqdesc.c b/kernel/irq/irqdesc.c
> > index a1782f8..bfbeeb6 100644
> > --- a/kernel/irq/irqdesc.c
> > +++ b/kernel/irq/irqdesc.c
> > @@ -365,7 +365,7 @@ int __handle_domain_irq(struct irq_domain 
> > *domain, unsigned int hwirq,
> >          * Some hardware gives randomly wrong interrupts.  Rather
> >          * than crashing, do something sensible.
> >          */
> > -       if (unlikely(!irq || irq >= nr_irqs)) {
> > +       if (unlikely(irq >= nr_irqs)) {
> >                 ack_bad_irq(irq);
> >                 ret = -EINVAL;
> >         } else {
> > 
> 
> Unfortunately, this is the wrong thing to do. IRQ0 is invalid, has been
> for a very long time, and actually represents the lack of interrupt.

OK, sorry for the mistake, I didn't know. Shouldn't the IRQ
initialization routine check this and warn the user that it may cause
problems? ?Silently? making IRQ0 forbidden doesn't help for the
platforms that are not fixed yet.

> The way you can address this is by making sure your favourite platform
> does not use IRQ0 at all, which is done by not assuming that Linux IRQ
> number (which is always completely virtual) is the same as the number
> designating the actual HW interrupt line.
>
> For example, have a look at 18f3aec (ARM: 8230/1: sa1100: shift IRQs by
> one) for an example of such a (very simple) conversion. You'll need to
> tweak irq.c too.
> 
> Other commits for sa1100 will hopefully convince you to switch to irq
> domains altogether. This will greatly facilitate a possible further
> transition to DT if you wish to do so.

I read quite a bit about all this virtual/hardware IRQ stuff, and the
irq domains, interesting. I see that orion5x seems to be one of the
last platforms not using it (appart from DT-converted boards); is it a
bad sign about its durability??

> Looking forward to reviewing your patches,

Thanks for your help and support. As the others suggested (thanks to
all of you too), I will try the DT way directly then.

Regards,
--
benjamin