xen/arm: smmu: Use writeq_relaxed_non_atomic() for writing to SMMU_CBn_TTBR0

Refer ARM IHI 0062D.c ID070116 (SMMU 2.0 spec), 17-360, 17.3.9,
SMMU_CBn_TTBR0 is a 64 bit register. Thus, one can use
writeq_relaxed_non_atomic() to write to it instead of invoking
writel_relaxed() twice for lower half and upper half of the register.

This also helps us as p2maddr is 'paddr_t' (which may be u32 in future).
Thus, one can assign p2maddr to a 64 bit register and do the bit
manipulations on it, to generate the value for SMMU_CBn_TTBR0.

Signed-off-by: Ayan Kumar Halder <ayan.kumar.halder@amd.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Reviewed-by: Michal Orzel <michal.orzel@amd.com>
Reviewed-by: Rahul Singh <rahul.singh@arm.com>

xen/drivers/passthrough/arm/smmu.c

@@ -499,8 +499,7 @@ enum arm_smmu_s2cr_privcfg {
 #define ARM_SMMU_CB_SCTLR		0x0
 #define ARM_SMMU_CB_RESUME		0x8
 #define ARM_SMMU_CB_TTBCR2		0x10
-#define ARM_SMMU_CB_TTBR0_LO		0x20
-#define ARM_SMMU_CB_TTBR0_HI		0x24
+#define ARM_SMMU_CB_TTBR0		0x20
 #define ARM_SMMU_CB_TTBCR		0x30
 #define ARM_SMMU_CB_S1_MAIR0		0x38
 #define ARM_SMMU_CB_FSR			0x58
@@ -1083,6 +1082,7 @@ static void arm_smmu_flush_pgtable(struct arm_smmu_device *smmu, void *addr,
 static void arm_smmu_init_context_bank(struct arm_smmu_domain *smmu_domain)
 {
 	u32 reg;
+	uint64_t reg64;
 	bool stage1;
 	struct arm_smmu_cfg *cfg = &smmu_domain->cfg;
 	struct arm_smmu_device *smmu = smmu_domain->smmu;
@@ -1177,12 +1177,13 @@ static void arm_smmu_init_context_bank(struct arm_smmu_domain *smmu_domain)
 	dev_notice(smmu->dev, "d%u: p2maddr 0x%"PRIpaddr"\n",
 		   smmu_domain->cfg.domain->domain_id, p2maddr);
 
-	reg = (p2maddr & ((1ULL << 32) - 1));
-	writel_relaxed(reg, cb_base + ARM_SMMU_CB_TTBR0_LO);
-	reg = (p2maddr >> 32);
+	reg64 = p2maddr;
+
 	if (stage1)
-		reg |= ARM_SMMU_CB_ASID(cfg) << TTBRn_HI_ASID_SHIFT;
-	writel_relaxed(reg, cb_base + ARM_SMMU_CB_TTBR0_HI);
+		reg64 |= (((uint64_t) (ARM_SMMU_CB_ASID(cfg) << TTBRn_HI_ASID_SHIFT))
+		          << 32);
+
+	writeq_relaxed_non_atomic(reg64, cb_base + ARM_SMMU_CB_TTBR0);
 
 	/*
 	 * TTBCR