iommu/ipmmu-vmsa: IMUCTRn.TTSEL needs a special usage on R-Car Gen3

The TTSEL bit of IMUCTRn register of R-Car Gen3 needs to be set
unused MMU context number even if uTLBs are disabled
(The MMUEN bit of IMUCTRn register = 0).
Since initial values of IMUCTRn.TTSEL on all IPMMU-domains are 0,
this patch adds a new feature "reserved_context" to reserve IPMMU
context number 0 as the unused MMU context.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/ipmmu-vmsa.c

@@ -47,6 +47,7 @@ struct ipmmu_features {
 	unsigned int number_of_contexts;
 	bool setup_imbuscr;
 	bool twobit_imttbcr_sl0;
+	bool reserved_context;
 };
 
 struct ipmmu_vmsa_device {
@@ -925,6 +926,7 @@ static const struct ipmmu_features ipmmu_features_default = {
 	.number_of_contexts = 1, /* software only tested with one context */
 	.setup_imbuscr = true,
 	.twobit_imttbcr_sl0 = false,
+	.reserved_context = false,
 };
 
 static const struct ipmmu_features ipmmu_features_rcar_gen3 = {
@@ -933,6 +935,7 @@ static const struct ipmmu_features ipmmu_features_rcar_gen3 = {
 	.number_of_contexts = 8,
 	.setup_imbuscr = false,
 	.twobit_imttbcr_sl0 = true,
+	.reserved_context = true,
 };
 
 static const struct of_device_id ipmmu_of_ids[] = {
@@ -1038,6 +1041,11 @@ static int ipmmu_probe(struct platform_device *pdev)
 		}
 
 		ipmmu_device_reset(mmu);
+
+		if (mmu->features->reserved_context) {
+			dev_info(&pdev->dev, "IPMMU context 0 is reserved\n");
+			set_bit(0, mmu->ctx);
+		}
 	}
 
 	/*