linux-kernel - Re: [PATCH] arm64/irq: report bug if NR_IPI greater than max SGI during compile time

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Date:   Tue, 8 Dec 2020 17:43:25 +0800
From:   Pingfan Liu <kernelfans@...il.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Mark Rutland <mark.rutland@....com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm64/irq: report bug if NR_IPI greater than max SGI
 during compile time

On Tue, Dec 8, 2020 at 5:31 PM Marc Zyngier <maz@...nel.org> wrote:
>
> On 2020-12-08 09:21, Pingfan Liu wrote:
> > Although there is a runtime WARN_ON() when NR_IPR > max SGI, it had
> > better
> > do the check during built time, and associate these related code
> > together.
> >
> > Signed-off-by: Pingfan Liu <kernelfans@...il.com>
> > Cc: Catalin Marinas <catalin.marinas@....com>
> > Cc: Will Deacon <will@...nel.org>
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > Cc: Jason Cooper <jason@...edaemon.net>
> > Cc: Marc Zyngier <maz@...nel.org>
> > Cc: Mark Rutland <mark.rutland@....com>
> > To: linux-arm-kernel@...ts.infradead.org
> > Cc: linux-kernel@...r.kernel.org
> > ---
> >  arch/arm64/kernel/smp.c                | 2 ++
> >  drivers/irqchip/irq-gic-v3.c           | 2 +-
> >  drivers/irqchip/irq-gic.c              | 2 +-
> >  include/linux/irqchip/arm-gic-common.h | 2 ++
> >  4 files changed, 6 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> > index 18e9727..9fc383c 100644
> > --- a/arch/arm64/kernel/smp.c
> > +++ b/arch/arm64/kernel/smp.c
> > @@ -33,6 +33,7 @@
> >  #include <linux/kernel_stat.h>
> >  #include <linux/kexec.h>
> >  #include <linux/kvm_host.h>
> > +#include <linux/irqchip/arm-gic-common.h>
> >
> >  #include <asm/alternative.h>
> >  #include <asm/atomic.h>
> > @@ -76,6 +77,7 @@ enum ipi_msg_type {
> >       IPI_WAKEUP,
> >       NR_IPI
> >  };
> > +static_assert(NR_IPI <= MAX_SGI_NUM);
>
> I am trying *very hard* to remove dependencies between the architecture
> code and random drivers, so this kind of check really is
> counter-productive.
>
> Driver code should not have to know the number of IPIs, because there is
> no requirement that all IPIs should map 1:1 to SGIs. Conflating the two

Just curious about this. Is there an IPI which is not implemented by
SGI? Or mapping several IPIs to a single SGI, and scatter out due to a
global variable value?

Thanks,
Pingfan

> is already wrong, and I really don't want to add more of that.
>
> Thanks,
>
>          M.
> --
> Jazz is not dead. It just smells funny...