iommu/arm-smmu: Warn once when the perfetcher errata patch fails to apply

Default reset value of secure banked register SMMU_sACR.cache_lock is 1.
If it is not been set to 0 by secure software(eg: atf), the non-secure
linux cannot clear ARM_MMU500_ACTLR_CPRE bit. In this situation,
the prefetcher errata is not applied successfully, warn once.
Signed-off-by: Chen Lin <chen45464546@163.com>
Link: https://lore.kernel.org/r/20221103222121.3051-1-chen45464546@163.com
[will: Tweaked wording of diagnostic]
Signed-off-by: Will Deacon <will@kernel.org>

drivers/iommu/arm/arm-smmu/arm-smmu-impl.c

@@ -136,6 +136,9 @@ int arm_mmu500_reset(struct arm_smmu_device *smmu)
 		reg = arm_smmu_cb_read(smmu, i, ARM_SMMU_CB_ACTLR);
 		reg &= ~ARM_MMU500_ACTLR_CPRE;
 		arm_smmu_cb_write(smmu, i, ARM_SMMU_CB_ACTLR, reg);
+		reg = arm_smmu_cb_read(smmu, i, ARM_SMMU_CB_ACTLR);
+		if (reg & ARM_MMU500_ACTLR_CPRE)
+			dev_warn_once(smmu->dev, "Failed to disable prefetcher [errata #841119 and #826419], check ACR.CACHE_LOCK\n");
 	}
 
 	return 0;