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@xxxxxxxxxxxx> Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx> --- Changes in v2: - "when CPUs are powered" => "when the GIC redistributors are..." - mediatek,gicr-save-quirk => mediatek,broken-save-restore-fw .../bindings/interrupt-controller/arm,gic-v3.yaml | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/Documentation/devicetree/bindings/interrupt-controller/arm,gic-v3.yaml b/Documentation/devicetree/bindings/interrupt-controller/arm,gic-v3.yaml index 92117261e1e1..39e64c7f6360 100644 --- a/Documentation/devicetree/bindings/interrupt-controller/arm,gic-v3.yaml +++ b/Documentation/devicetree/bindings/interrupt-controller/arm,gic-v3.yaml @@ -166,6 +166,12 @@ properties: resets: maxItems: 1 + mediatek,broken-save-restore-fw: + type: boolean + description: + Asserts that the firmware on this device has issues saving and restoring + GICR registers when the GIC redistributors are powered off. + dependencies: mbi-ranges: [ msi-controller ] msi-controller: [ mbi-ranges ] -- 2.40.1.606.ga4b1b128d6-goog
