[PATCH 1/2] dt-bindings: arm-smmu: Add qcom,last-ctx-bank-reserved

From: Marc Gonzalez
Date: Wed Aug 14 2024 - 10:00:34 EST


On qcom msm8998, writing to the last context bank of lpass_q6_smmu
(base address 0x05100000) produces a system freeze & reboot.

Specifically, here:

qsmmu->bypass_cbndx = smmu->num_context_banks - 1;
arm_smmu_cb_write(smmu, qsmmu->bypass_cbndx, ARM_SMMU_CB_SCTLR, 0);

and here:

arm_smmu_write_context_bank(smmu, i);
arm_smmu_cb_write(smmu, i, ARM_SMMU_CB_FSR, ARM_SMMU_CB_FSR_FAULT);

It is likely that FW reserves the last context bank for its own use,
thus a simple work-around would be: DON'T USE IT in Linux.

Signed-off-by: Marc Gonzalez <mgonzalez@xxxxxxxxxx>
---
Documentation/devicetree/bindings/iommu/arm,smmu.yaml | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/Documentation/devicetree/bindings/iommu/arm,smmu.yaml b/Documentation/devicetree/bindings/iommu/arm,smmu.yaml
index 280b4e49f2191..f9b23aef351b0 100644
--- a/Documentation/devicetree/bindings/iommu/arm,smmu.yaml
+++ b/Documentation/devicetree/bindings/iommu/arm,smmu.yaml
@@ -204,6 +204,12 @@ properties:
access to SMMU configuration registers. In this case non-secure aliases of
secure registers have to be used during SMMU configuration.

+ qcom,last-ctx-bank-reserved:
+ type: boolean
+ description:
+ FW reserves the last context bank of this SMMU for its own use.
+ If Linux tries to use it, Linux gets nuked.
+
stream-match-mask:
$ref: /schemas/types.yaml#/definitions/uint32
description: |

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2.34.1