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 18:00:12 +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>,
        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 5:51 PM Marc Zyngier <maz@...nel.org> wrote:
>
> On 2020-12-08 09:43, Pingfan Liu wrote:
> > 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?
>
> We currently have a single NS SGI left, and I'd like to move some of the
> non-critical IPIs over to dispatching mechanism (the two "CPU stop" IPIs
> definitely are candidate for merging). That's not implemented yet, but
> I don't see a need to add checks that would otherwise violate this
> IPI/SGI distinction.

Got it. Thanks for your detailed explanation.

Regards,
Pingfan