iommu/arm-smmu: Allow implementation specific write_s2cr

The firmware found in some Qualcomm platforms intercepts writes to the
S2CR register in order to replace the BYPASS type with FAULT. Further
more it treats faults at this level as catastrophic and restarts the
device.

Add support for providing implementation specific versions of the S2CR
write function, to allow the Qualcomm driver to work around this
behavior.

Cc: <stable@vger.kernel.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Tested-by: Steev Klimaszewski <steev@kali.org>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/20201019182323.3162386-2-bjorn.andersson@linaro.orgSigned-off-by: Will Deacon <will@kernel.org>

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

@@ -929,9 +929,16 @@ static void arm_smmu_write_smr(struct arm_smmu_device *smmu, int idx)
 static void arm_smmu_write_s2cr(struct arm_smmu_device *smmu, int idx)
 {
 	struct arm_smmu_s2cr *s2cr = smmu->s2crs + idx;
-	u32 reg = FIELD_PREP(ARM_SMMU_S2CR_TYPE, s2cr->type) |
-		  FIELD_PREP(ARM_SMMU_S2CR_CBNDX, s2cr->cbndx) |
-		  FIELD_PREP(ARM_SMMU_S2CR_PRIVCFG, s2cr->privcfg);
+	u32 reg;
+
+	if (smmu->impl && smmu->impl->write_s2cr) {
+		smmu->impl->write_s2cr(smmu, idx);
+		return;
+	}
+
+	reg = FIELD_PREP(ARM_SMMU_S2CR_TYPE, s2cr->type) |
+	      FIELD_PREP(ARM_SMMU_S2CR_CBNDX, s2cr->cbndx) |
+	      FIELD_PREP(ARM_SMMU_S2CR_PRIVCFG, s2cr->privcfg);
 
 	if (smmu->features & ARM_SMMU_FEAT_EXIDS && smmu->smrs &&
 	    smmu->smrs[idx].valid)

drivers/iommu/arm/arm-smmu/arm-smmu.h

@@ -436,6 +436,7 @@ struct arm_smmu_impl {
 	int (*alloc_context_bank)(struct arm_smmu_domain *smmu_domain,
 				  struct arm_smmu_device *smmu,
 				  struct device *dev, int start);
+	void (*write_s2cr)(struct arm_smmu_device *smmu, int idx);
 };
 
 #define INVALID_SMENDX			-1