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

[Marc Zyngier]

On 2020-12-08 09:43, Pingfan Liu wrote:
> On Tue, Dec 8, 2020 at 5:31 PM Marc Zyngier <maz@xxxxxxxxxx> 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@xxxxxxxxx>
> > > Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> > > Cc: Will Deacon <will@xxxxxxxxxx>
> > > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > > Cc: Jason Cooper <jason@xxxxxxxxxxxxxx>
> > > Cc: Marc Zyngier <maz@xxxxxxxxxx>
> > > Cc: Mark Rutland <mark.rutland@xxxxxxx>
> > > To: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> > > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > > ---
> > >  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.

Thanks,

         M.
--
Jazz is not dead. It just smells funny...