[PATCH 0/2] Work around reserved SMMU context bank on msm8998

[Marc Gonzalez]

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.

This patch series:
1) introduces a DT prop "qcom,last-ctx-bank-reserved" to indicate
that FW reserves the last context bank of a given SMMU.
2) tweaks the driver to "hide" the last context bank from Linux.

For reference, the lpass_q6_smmu node looks like this:

	lpass_q6_smmu: iommu@5100000 {
		compatible = "qcom,msm8998-smmu-v2", "qcom,smmu-v2";
		reg = <0x05100000 0x40000>;
		clocks = <&gcc HLOS1_VOTE_LPASS_ADSP_SMMU_CLK>;
		clock-names = "iface";

		#global-interrupts = <0>;
		#iommu-cells = <1>;
		interrupts =
			<GIC_SPI 226 IRQ_TYPE_LEVEL_HIGH>,
			<GIC_SPI 393 IRQ_TYPE_LEVEL_HIGH>,
			<GIC_SPI 394 IRQ_TYPE_LEVEL_HIGH>,
			<GIC_SPI 395 IRQ_TYPE_LEVEL_HIGH>,
			<GIC_SPI 396 IRQ_TYPE_LEVEL_HIGH>,
			<GIC_SPI 397 IRQ_TYPE_LEVEL_HIGH>,
			<GIC_SPI 398 IRQ_TYPE_LEVEL_HIGH>,
			<GIC_SPI 399 IRQ_TYPE_LEVEL_HIGH>,
			<GIC_SPI 400 IRQ_TYPE_LEVEL_HIGH>,
			<GIC_SPI 401 IRQ_TYPE_LEVEL_HIGH>,
			<GIC_SPI 402 IRQ_TYPE_LEVEL_HIGH>,
			<GIC_SPI 403 IRQ_TYPE_LEVEL_HIGH>,
			<GIC_SPI 137 IRQ_TYPE_LEVEL_HIGH>;

		power-domains = <&gcc LPASS_ADSP_GDSC>;
		status = "disabled";
	};

---
Marc Gonzalez (2):
      dt-bindings: arm-smmu: Add qcom,last-ctx-bank-reserved
      iommu/arm-smmu-qcom: hide last context bank from linux

 Documentation/devicetree/bindings/iommu/arm,smmu.yaml | 6 ++++++
 drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c            | 5 +++++
 2 files changed, 11 insertions(+)
---
base-commit: c934f6908ad1f210c1d1e289934d1182a6e7cb62
change-id: 20240814-smmu-d572c1a16aac

Best regards,
-- 
Marc Gonzalez <mgonzalez@xxxxxxxxxx>