linux-kernel - Re: [PATCH AUTOSEL 6.3 12/37] irqchip/gic-v3: Disable pseudo NMIs on Mediatek devices w/ firmware issues

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Date:   Wed, 31 May 2023 06:58:35 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Sasha Levin <sashal@...nel.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Julius Werner <jwerner@...omium.org>,
        Marc Zyngier <maz@...nel.org>, tglx@...utronix.de,
        matthias.bgg@...il.com, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH AUTOSEL 6.3 12/37] irqchip/gic-v3: Disable pseudo NMIs on
 Mediatek devices w/ firmware issues

Hi,

On Wed, May 31, 2023 at 6:40 AM Sasha Levin <sashal@...nel.org> wrote:
>
> From: Douglas Anderson <dianders@...omium.org>
>
> [ Upstream commit 44bd78dd2b8897f59b7e3963f088caadb7e4f047 ]
>
> Some Chromebooks with Mediatek SoCs have a problem where the firmware
> doesn't properly save/restore certain GICR registers. Newer
> Chromebooks should fix this issue and we may be able to do firmware
> updates for old Chromebooks. At the moment, the only known issue with
> these Chromebooks is that we can't enable "pseudo NMIs" since the
> priority register can be lost. Enabling "pseudo NMIs" on Chromebooks
> with the problematic firmware causes crashes and freezes.
>
> Let's detect devices with this problem and then disable "pseudo NMIs"
> on them. We'll detect the problem by looking for the presence of the
> "mediatek,broken-save-restore-fw" property in the GIC device tree
> node. Any devices with fixed firmware will not have this property.
>
> Our detection plan works because we never bake a Chromebook's device
> tree into firmware. Instead, device trees are always bundled with the
> kernel. We'll update the device trees of all affected Chromebooks and
> then we'll never enable "pseudo NMI" on a kernel that is bundled with
> old device trees. When a firmware update is shipped that fixes this
> issue it will know to patch the device tree to remove the property.
>
> In order to make this work, the quick detection mechanism of the GICv3
> code is extended to be able to look for properties in addition to
> looking at "compatible".
>
> Reviewed-by: Julius Werner <jwerner@...omium.org>
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> Signed-off-by: Marc Zyngier <maz@...nel.org>
> Link: https://lore.kernel.org/r/20230515131353.v2.2.I88dc0a0eb1d9d537de61604cd8994ecc55c0cac1@changeid
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---
>  drivers/irqchip/irq-gic-common.c |  8 ++++++--
>  drivers/irqchip/irq-gic-common.h |  1 +
>  drivers/irqchip/irq-gic-v3.c     | 20 ++++++++++++++++++++
>  3 files changed, 27 insertions(+), 2 deletions(-)

Please delay picking this across all stable versions unless until you
can also get Marc's fix:

https://lore.kernel.org/r/168544149933.404.717399647227994720.tip-bot2@tip-bot2

-Doug