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From:   Doug Anderson <dianders@chromium.org>
Date:   Wed, 4 Oct 2023 07:04:12 -0700
Message-ID: <CAD=FV=XasZR6dhKBjpbYfby4F1Nu_bsq1m_HP+NpufjsJi0COg@mail.gmail.com>
Subject: Re: [PATCH 1/2] arm64: smp: Fix pseudo NMI issues w/ broken Mediatek FW
To:     Marc Zyngier <maz@kernel.org>
Cc:     Mark Rutland <mark.rutland@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Stephen Boyd <swboyd@chromium.org>,
        Valentin Schneider <vschneid@redhat.com>,
        Chen-Yu Tsai <wenst@chromium.org>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@collabora.com>,
        D Scott Phillips <scott@os.amperecomputing.com>,
        Josh Poimboeuf <jpoimboe@kernel.org>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Misono Tomohiro <misono.tomohiro@fujitsu.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Sumit Garg <sumit.garg@linaro.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-mediatek@lists.infradead.org
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Hi,

On Wed, Oct 4, 2023 at 3:15=E2=80=AFAM Marc Zyngier <maz@kernel.org> wrote:
>
> On Wed, 04 Oct 2023 10:59:50 +0100,
> Mark Rutland <mark.rutland@arm.com> wrote:
> >
> > Given you haven't seen any issues, I suspect those are getting reset to=
 fixed
> > values that happens to work out for us, but it is a bit worrisome more
> > generally (e.g. the LPI case above).
>
> It is likely that these SoCs don't even have an ITS.

Right. That was what we decided [1] when Marc pointed this out earlier.

Overall: we know that this firmware behavior is not good but we're
stuck with it. :( At the very least, any new devices coming out will
have this fixed. Presumably if old devices are working OK enough today
(as long as you don't enable pseudo-NMI) then they can be made to keep
working?

So circling back: what patch should we actually land? As of right now
only pseudo-NMI is broken, but it would be good to make sure that if
the kernel later adds other features that would be broken on this
hardware that it gets handled properly...

[1] https://issuetracker.google.com/issues/281831288#comment4