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Date:   Wed, 11 Sep 2019 16:40:43 +0200
From:   Greg Kurz <groug@kaod.org>
To:     Michael Ellerman <mpe@ellerman.id.au>
Cc:     Paul Mackerras <paulus@ozlabs.org>,
        =?UTF-8?B?Q8OpZHJpYw==?= Le Goater <clg@kaod.org>,
        David Gibson <david@gibson.dropbear.id.au>,
        linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] powerpc/xive: Fix bogus error code returned by OPAL
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On Thu, 12 Sep 2019 00:26:19 +1000
Michael Ellerman <mpe@ellerman.id.au> wrote:

> Hi Greg,
> 

Bom dia ! :)

> Couple of comments ...
> 
> Greg Kurz <groug@kaod.org> writes:
> > There's a bug in skiboot that causes the OPAL_XIVE_ALLOCATE_IRQ call
> > to return the 32-bit value 0xffffffff when OPAL has run out of IRQs.
> > Unfortunatelty, OPAL return values are signed 64-bit entities and
> > errors are supposed to be negative. If that happens, the linux code
> > confusingly treats 0xffffffff as a valid IRQ number and panics at some
> > point.
> >
> > A fix was recently merged in skiboot:
> >
> > e97391ae2bb5 ("xive: fix return value of opal_xive_allocate_irq()")
> >
> > but we need a workaround anyway to support older skiboots already
> > on the field.
>   ^
>   in
>  
> >
> > Internally convert 0xffffffff to OPAL_RESOURCE which is the usual error
> > returned upon resource exhaustion.
> 
> This should go to stable, any idea what versions it should go back to?
> Probably whenever the xive code was introduced?
> 

Yes I guess so. This would mean v4.12. I'll add the appropriate stable
tag before re-posting, and address all the other remarks of course.

> > Signed-off-by: Greg Kurz <groug@kaod.org>
> > ---
> >  arch/powerpc/sysdev/xive/native.c |   13 +++++++++++--
> >  1 file changed, 11 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/powerpc/sysdev/xive/native.c b/arch/powerpc/sysdev/xive/native.c
> > index 37987c815913..c35583f84f9f 100644
> > --- a/arch/powerpc/sysdev/xive/native.c
> > +++ b/arch/powerpc/sysdev/xive/native.c
> > @@ -231,6 +231,15 @@ static bool xive_native_match(struct device_node *node)
> >  	return of_device_is_compatible(node, "ibm,opal-xive-vc");
> >  }
> >  
> > +static int64_t opal_xive_allocate_irq_fixup(uint32_t chip_id)
>           ^                                    ^
>           Can you use s64 here and u32 here ....
> 
> Instead of calling this opal_xive_allocate_irq_fixup() and relying on
> all callers to call the fixup, can we rename the opal wrapper and leave
> this function's name unchanged, eg:
> 
> -OPAL_CALL(opal_xive_allocate_irq,              OPAL_XIVE_ALLOCATE_IRQ);
> +OPAL_CALL(opal_xive_allocate_irq_raw,          OPAL_XIVE_ALLOCATE_IRQ);
> 
> 
> > +{
> > +	s64 irq = opal_xive_allocate_irq(chip_id);
> > +
> > +#define XIVE_ALLOC_NO_SPACE	0xffffffff /* No possible space */
> > +	return
> > +		irq == XIVE_ALLOC_NO_SPACE ? OPAL_RESOURCE : irq;
> > +}
> 
> I don't really like the #define and the weird indenting and so on, can
> we instead do it like:
> 
> 	/*
>          * Old versions of skiboot can incorrectly return 0xffffffff to
>          * indicate no space, fix it up here.
>          */
> 	return irq == 0xffffffff ? OPAL_RESOURCE : irq;
> 
> cheers