iommu/arm-smmu-v3: limit use of 2-level stream tables

In the current arm-smmu-v3 driver, all smmus that support 2-level
stream tables are being forced to use them. This is suboptimal for
smmus that support fewer stream id bits than would fill in a single
second level table. This patch limits the use of 2-level tables to
smmus that both support the feature and whose first level table can
possibly contain more than a single entry.

Signed-off-by: Nate Watterson <nwatters@codeaurora.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>

drivers/iommu/arm-smmu-v3.c

@@ -1977,17 +1977,9 @@ static int arm_smmu_init_strtab_2lvl(struct arm_smmu_device *smmu)
 	u32 size, l1size;
 	struct arm_smmu_strtab_cfg *cfg = &smmu->strtab_cfg;
 
-	/*
-	 * If we can resolve everything with a single L2 table, then we
-	 * just need a single L1 descriptor. Otherwise, calculate the L1
-	 * size, capped to the SIDSIZE.
-	 */
-	if (smmu->sid_bits < STRTAB_SPLIT) {
-		size = 0;
-	} else {
-		size = STRTAB_L1_SZ_SHIFT - (ilog2(STRTAB_L1_DESC_DWORDS) + 3);
-		size = min(size, smmu->sid_bits - STRTAB_SPLIT);
-	}
+	/* Calculate the L1 size, capped to the SIDSIZE. */
+	size = STRTAB_L1_SZ_SHIFT - (ilog2(STRTAB_L1_DESC_DWORDS) + 3);
+	size = min(size, smmu->sid_bits - STRTAB_SPLIT);
 	cfg->num_l1_ents = 1 << size;
 
 	size += STRTAB_SPLIT;
@@ -2498,6 +2490,13 @@ static int arm_smmu_device_hw_probe(struct arm_smmu_device *smmu)
 	smmu->ssid_bits = reg >> IDR1_SSID_SHIFT & IDR1_SSID_MASK;
 	smmu->sid_bits = reg >> IDR1_SID_SHIFT & IDR1_SID_MASK;
 
+	/*
+	 * If the SMMU supports fewer bits than would fill a single L2 stream
+	 * table, use a linear table instead.
+	 */
+	if (smmu->sid_bits <= STRTAB_SPLIT)
+		smmu->features &= ~ARM_SMMU_FEAT_2_LVL_STRTAB;
+
 	/* IDR5 */
 	reg = readl_relaxed(smmu->base + ARM_SMMU_IDR5);