linux-kernel - Re: [PATCH v2 1/5] dt-bindings: interrupt-controller: arm,gic-v3: Add quirk for Mediatek SoCs w/ broken FW

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Message-ID: <30766850-b4c7-3ea2-fadf-3d67855107e1@collabora.com>
Date:   Tue, 16 May 2023 15:24:18 +0200
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Douglas Anderson <dianders@...omium.org>,
        Marc Zyngier <maz@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Matthias Brugger <matthias.bgg@...il.com>
Cc:     devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Allen-KH Cheng <allen-kh.cheng@...iatek.com>,
        linux-mediatek@...ts.infradead.org,
        Eddie Huang <eddie.huang@...iatek.com>,
        Hsin-Hsiung Wang <hsin-hsiung.wang@...iatek.com>,
        wenst@...omium.org, yidilin@...omium.org,
        Tinghan Shen <tinghan.shen@...iatek.com>, jwerner@...omium.org,
        Weiyi Lu <weiyi.lu@...iatek.com>, Ben Ho <Ben.Ho@...iatek.com>,
        Seiya Wang <seiya.wang@...iatek.com>,
        Conor Dooley <conor+dt@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/5] dt-bindings: interrupt-controller: arm,gic-v3: Add
 quirk for Mediatek SoCs w/ broken FW

Il 15/05/23 22:13, Douglas Anderson ha scritto:
> When trying to turn on the "pseudo NMI" kernel feature in Linux, it
> was discovered that all Mediatek-based Chromebooks that ever shipped
> (at least ones with GICv3) had a firmware bug where they wouldn't save
> certain GIC "GICR" registers properly. If a processor ever entered a
> suspend/idle mode where the GICR registers lost state then they'd be
> reset to their default state.
> 
> As a result of the bug, if you try to enable "pseudo NMIs" on the
> affected devices then certain interrupts will unexpectedly get
> promoted to be "pseudo NMIs" and cause crashes / freezes / general
> mayhem.
> 
> ChromeOS is looking to start turning on "pseudo NMIs" in production to
> make crash reports more actionable. To do so, we will release firmware
> updates for at least some of the affected Mediatek Chromebooks.
> However, even when we update the firmware of a Chromebook it's always
> possible that a user will end up booting with old firmware. We need to
> be able to detect when we're running with firmware that will crash and
> burn if pseudo NMIs are enabled.
> 
> The current plan is:
> * Update the device trees of all affected Chromebooks to include the
>    'mediatek,broken-save-restore-fw' property. The kernel can use this
>    to know not to enable certain features like "pseudo NMI". NOTE:
>    device trees for Chromebooks are never baked into the firmware but
>    are bundled with the kernel. A kernel will never be configured to
>    use "pseudo NMIs" and be bundled with an old device tree.
> * When we get a fixed firmware for one of these Chromebooks, it will
>    patch the device tree to remove this property.
> 
> For some details, you can also see the public bug
> <https://issuetracker.google.com/281831288>
> 
> Reviewed-by: Julius Werner <jwerner@...omium.org>
> Signed-off-by: Douglas Anderson <dianders@...omium.org>

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>