linux-kernel - [PATCH v4 1/2] iommu/arm-smmu-v3: Add boolean bypass_ste and skip

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Message-ID: <45b65b0a774068be805b7e1b45063fe10ec51d3a.1695242337.git.nicolinc@nvidia.com>
Date:   Wed, 20 Sep 2023 13:52:03 -0700
From:   Nicolin Chen <nicolinc@...dia.com>
To:     <will@...nel.org>, <robin.murphy@....com>, <jgg@...dia.com>
CC:     <joro@...tes.org>, <jean-philippe@...aro.org>,
        <mshavit@...gle.com>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <iommu@...ts.linux.dev>
Subject: [PATCH v4 1/2] iommu/arm-smmu-v3: Add boolean bypass_ste and skip_cdtab flags

If a master has only a default substream, it can skip CD/translation table
allocations when being attached to an IDENTITY domain, by simply setting
STE to the "bypass" mode (STE.Config[2:0] == 0b100).

If a master has multiple substreams, it will still need a CD table for the
non-default substreams when being attached to an IDENTITY domain, in which
case the STE.Config is set to the "stage-1 translate" mode while STE.S1DSS
field instead is set to the "bypass" mode (STE.S1DSS[1:0] == 0b01).

If a master is attached to a stage-2 domain, it does not need a CD table,
while the STE.Config is set to the "stage-2 translate" mode.

Add boolean bypass_ste and skip_cdtab flags in arm_smmu_attach_dev(), to
handle clearly the cases above, which also corrects the conditions at the
ats_enabled setting and arm_smmu_alloc_cd_tables() callback to cover the
second use case.

Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
---
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 35 ++++++++++++++++-----
 1 file changed, 27 insertions(+), 8 deletions(-)

diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
index df6409017127..dbe11997b4b9 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -2381,6 +2381,7 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
 	struct arm_smmu_device *smmu;
 	struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
 	struct arm_smmu_master *master;
+	bool byapss_ste, skip_cdtab;
 
 	if (!fwspec)
 		return -ENOENT;
@@ -2416,6 +2417,24 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
 
 	master->domain = smmu_domain;
 
+	/*
+	 * When master attaches ARM_SMMU_DOMAIN_BYPASS to its single substream,
+	 * set STE.Config to "bypass" and skip a CD table allocation. Otherwise,
+	 * set STE.Config to "stage-1 translate" and allocate a CD table for its
+	 * multiple stage-1 substream support, unless with a stage-2 domain in
+	 * which case set STE.config to "stage-2 translate" and skip a CD table.
+	 */
+	if (smmu_domain->stage == ARM_SMMU_DOMAIN_BYPASS && !master->ssid_bits) {
+		byapss_ste = true;
+		skip_cdtab = true;
+	} else {
+		byapss_ste = false;
+		if (smmu_domain->stage == ARM_SMMU_DOMAIN_S2)
+			skip_cdtab = true;
+		else
+			skip_cdtab = false;
+	}
+
 	/*
 	 * The SMMU does not support enabling ATS with bypass. When the STE is
 	 * in bypass (STE.Config[2:0] == 0b100), ATS Translation Requests and
@@ -2423,22 +2442,22 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
 	 * stream (STE.EATS == 0b00), causing F_BAD_ATS_TREQ and
 	 * F_TRANSL_FORBIDDEN events (IHI0070Ea 5.2 Stream Table Entry).
 	 */
-	if (smmu_domain->stage != ARM_SMMU_DOMAIN_BYPASS)
+	if (!byapss_ste)
 		master->ats_enabled = arm_smmu_ats_supported(master);
 
 	spin_lock_irqsave(&smmu_domain->devices_lock, flags);
 	list_add(&master->domain_head, &smmu_domain->devices);
 	spin_unlock_irqrestore(&smmu_domain->devices_lock, flags);
 
-	if (smmu_domain->stage == ARM_SMMU_DOMAIN_S1) {
-		if (!master->cd_table.cdtab) {
-			ret = arm_smmu_alloc_cd_tables(master);
-			if (ret) {
-				master->domain = NULL;
-				goto out_list_del;
-			}
+	if (!skip_cdtab && !master->cd_table.cdtab) {
+		ret = arm_smmu_alloc_cd_tables(master);
+		if (ret) {
+			master->domain = NULL;
+			goto out_list_del;
 		}
+	}
 
+	if (smmu_domain->stage == ARM_SMMU_DOMAIN_S1) {
 		/*
 		 * Prevent SVA from concurrently modifying the CD or writing to
 		 * the CD entry
-- 
2.42.0