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

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Message-Id: <20240814-smmu-v1-1-3d6c27027d5b@freebox.fr>
Date: Wed, 14 Aug 2024 15:59:55 +0200
From: Marc Gonzalez <mgonzalez@...ebox.fr>
To: Rob Clark <robdclark@...il.com>, Will Deacon <will@...nel.org>, 
 Robin Murphy <robin.murphy@....com>, Joerg Roedel <joro@...tes.org>, 
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
 Conor Dooley <conor+dt@...nel.org>
Cc: iommu@...ts.linux.dev, linux-arm-msm@...r.kernel.org, 
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
 devicetree@...r.kernel.org, Bjorn Andersson <andersson@...nel.org>, 
 Konrad Dybcio <konradybcio@...nel.org>, Arnaud Vrac <avrac@...ebox.fr>, 
 Pierre-Hugues Husson <phhusson@...ebox.fr>, 
 Marijn Suijten <marijn.suijten@...ainline.org>, 
 Marc Gonzalez <mgonzalez@...ebox.fr>
Subject: [PATCH 1/2] dt-bindings: arm-smmu: Add qcom,last-ctx-bank-reserved

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@...ebox.fr>
---
 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: |

-- 
2.34.1