linux-kernel - Re: [RFC Patch v1 2/4] irqchip/gic-v3: Add support to handle SGI as pseudo NMI

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Message-ID: <CAFA6WYO3=BHX1exF+J=93ECnQFe3S5O4HrT4t14euw3t9PXE7A@mail.gmail.com>
Date:   Wed, 13 May 2020 15:32:36 +0530
From:   Sumit Garg <sumit.garg@...aro.org>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Daniel Thompson <daniel.thompson@...aro.org>,
        Jason Cooper <jason@...edaemon.net>,
        Catalin Marinas <catalin.marinas@....com>,
        Douglas Anderson <dianders@...omium.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Jason Wessel <jason.wessel@...driver.com>,
        kgdb-bugreport@...ts.sourceforge.net,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>, julien.thierry.kdev@...il.com
Subject: Re: [RFC Patch v1 2/4] irqchip/gic-v3: Add support to handle SGI as
 pseudo NMI

Hi Marc,

On Tue, 5 May 2020 at 17:03, Sumit Garg <sumit.garg@...aro.org> wrote:
>
> On Tue, 5 May 2020 at 15:38, Marc Zyngier <maz@...nel.org> wrote:
> >
> > On 2020-05-05 05:09, Sumit Garg wrote:
> > > On Fri, 1 May 2020 at 18:33, Sumit Garg <sumit.garg@...aro.org> wrote:
> >
> > [...]
> >
> > > In case there are no major objections to this approach, I will post
> > > complete v2 patch-set (alongwith Marc's patches) for detailed review.
> >
> > As this is still a work in progress (I'm currently wrestling with
> > the stupid RPi driver), whatever you have is unlikely to apply on
> > top of the final series.
> >
> > I'm not going to stop you from posting the patches, it is just that
> > they will be obsolete by the end of the week...
>
> Thanks for the heads up. Will wait for your final series.
>

Were you able to give a final shape to your SGIs related patch-set?

-Sumit

> But while working on an NMI request, I noticed a hack in common gic
> code [1] which basically enables all SGIs for every CPU by default.
> This hack is quite similar to mine initial hack to set priority for a
> particular SGI by default to act as pseudo NMI.
>
> Due to this hack I got following error message while configuring SGI as NMI:
>
> [    0.000000] GICv3: Cannot set NMI property of enabled IRQ 8
> [    0.000000] genirq: Failed to setup NMI delivery: irq 8
>
> I think chained IRQs worked for you due to this hack only as it
> doesn't seem to enable SGIs per CPU.
>
> IMO, as we shift to SGIs being standard interrupts, we should also
> rely on standard interrupt framework to enable SGIs. So it seems the
> correct way would be to use "request_percpu_irq()" and
> "enable_percpu_irq()" for configuring SGIs as demonstrated in updated
> commit here [2].
>
> Also, we should get rid of this hack as demonstrated via commit [3].
>
> Apart from above changes, there was a minor update needed for commit
> "irqchip/gic-v3: Describe the SGI range" [4].
>
> I hope these updates are useful for you while preparing the final series.
>
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/irqchip/irq-gic-common.c#n155
> [2] https://git.linaro.org/people/sumit.garg/linux.git/commit/?h=kgdb-nmi&id=e208979b5165d753d144db57e0cb8646fdedc495
> [3] https://git.linaro.org/people/sumit.garg/linux.git/commit/?h=kgdb-nmi&id=cd6d0d7cea14ac16156f0dbd297940df382f8cea
> [4] https://git.linaro.org/people/sumit.garg/linux.git/commit/?h=kgdb-nmi&id=1180e9c54547ec05d96cc6b36c26005059c90d9a
>
> -Sumit
>
> >
> > Thanks,
> >
> >          M.
> > --
> > Jazz is not dead. It just smells funny...