linux-kernel - Re: [PATCH v3 1/1] soc: fujitsu: Add A64FX diagnostic interrupt driver

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Message-ID: <CAK8P3a3v4+AO5avGoxeZSyNTOWqk8YS95xQLWSBZ=yV_3DKggg@mail.gmail.com>
Date:   Fri, 8 Apr 2022 16:49:31 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Hitomi Hasegawa <hasegawa-hitomi@...itsu.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        SoC Team <soc@...nel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        Sumit Garg <sumit.garg@...aro.org>,
        Olof Johansson <olof@...om.net>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Jason Wessel <jason.wessel@...driver.com>,
        Doug Anderson <dianders@...omium.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        kgdb-bugreport@...ts.sourceforge.net,
        Peter Zijlstra <peterz@...radead.org>,
        Mike Travis <mike.travis@....com>
Subject: Re: [PATCH v3 1/1] soc: fujitsu: Add A64FX diagnostic interrupt driver

On Fri, Apr 8, 2022 at 4:21 PM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Fri, Apr 08, 2022 at 04:17:16PM +0200, Arnd Bergmann wrote:
> > On Fri, Apr 8, 2022 at 3:32 PM Daniel Thompson
> > <daniel.thompson@...aro.org> wrote:
> > > On Thu, Mar 31, 2022 at 05:44:55PM +0200, Arnd Bergmann wrote:
> > >
> > > There is some prior art for this sort of feature. AFAICT SGI UV has a
> > > similar mechanism that can send an NMI-with-no-side-channel to the
> > > kernel. The corresponding driver offers a range of actions using a
> > > module parameter:
> > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/x86/platform/uv/uv_nmi.c#n180
> > >
> > > I don't think a hardcoded 'c' makes any sense. With a hardcoded argument
> > > it is just obfuscation. However it is certainly seems attractive to be
> > > able to reuse handle_sysrq() to provide a more powerful set of actions.
> >
> > How about a module parameter that allows picking a sysrq character then?
>
> Module parameters are so 1990, as this is a platform device, why not get
> it from DT?

This machine doesn't use DT. I suppose the same could be done with an EFI
variable, but with a module parameter you get the added benefit of having both
a boot time kernel command line argument, and the option to override it at
run time.

         Arnd