linux-kernel - Re: [PATCH v2 2/5] irqchip/gic-v3: Disable pseudo NMIs on Mediatek devices w/ firmware issues

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Date:   Tue, 16 May 2023 15:23:52 +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>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/5] irqchip/gic-v3: Disable pseudo NMIs on Mediatek
 devices w/ firmware issues

Il 15/05/23 22:13, Douglas Anderson ha scritto:
> 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>

I don't like firmware removing properties from my devicetrees and I'd like this
issue to get addressed in another way (use a scratch register? and check it in
Linux drivers to determine if the issue is not present: if scratch contains BIT(x),
do not parse the quirk) but that's a different discussion which is a bit out of
context for this patch, so:

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