[PATCH] soc: fujitsu: Add A64FX diagnostic interrupt driver

[Sumit Garg]

Hi Arnd, Hitomi,

On Fri, 25 Feb 2022 at 16:50, Arnd Bergmann <arnd at arndb.de> wrote:
>
> On Fri, Feb 25, 2022 at 11:35 AM hasegawa-hitomi at fujitsu.com
> <hasegawa-hitomi at fujitsu.com> wrote:
> >
> > Hi Greg and Jiri,
> >
> > I'm trying to implement a feature for A64FX that will panic when
> > a diagnostic interrupt is received.
> > Arnd suggested that handle_sysrq() should be used
> > but I'm wonderingif it's ok to call it in NMI.
> > Would you please let me know if we can call handle_sysrq() in NMI?
>
> I see some work from Sumit Garg to make it possible, but this was never
> merged, so presumably it is not safe:
>
> https://lore.kernel.org/linux-arm-kernel/CAFA6WYOWHgmYYt=KGXDh2hKiuy_rQbJfi279ev0+s-Qh7L21kA@mail.gmail.com/t/#m2b5006f08581448020eb24566927a104d0b95c44
>

Yeah it had some tricky bits but it wasn't the reason for the work
being stalled. Actually it turned out to be cumbersome to allow all
8250 UARTs to be driven from NMI interrupts as well. But given this
special diagnostic interrupt on A64FX turned as pseudo NMI, it
shouldn't be that hard to test it with this [1] minimal patch.

[1] https://lkml.org/lkml/2022/2/28/83

-Sumit

> Sumit has worked on some related areas as well, and may have additional
> ideas for you.
>
>         Arnd