[PATCH RFC v5 4/6] iommu/arm-smmu-v3: Support shared SIDs in insert/remove_master

["Peng Fan (OSS)" <peng.fan@oss.nxp.com>]

From: Peng Fan <peng.fan@nxp.com>

On SoCs like NXP i.MX95 where the SMMU has a limited number of Stream
IDs (e.g. 6-bit bus = 64 SIDs), multiple DMA-capable devices are
assigned the same Stream ID by hardware design.

Refactor arm_smmu_find_master() into arm_smmu_find_stream() to look up
streams by SID inside the lock. When a second master attempts to use a
SID that is already claimed, link the masters together via the stream's
shared_masters list instead of rejecting the probe.

Sharing is restricted to single-SID masters (num_streams == 1) to keep
the STE lifecycle simple. Multi-SID sharing is explicitly rejected.

On removal, a shared master detaches from the shared_masters list. The
stream and its RB tree entry are kept alive until the last master using
that SID is removed.

Suggested-by: Nicolin Chen <nicolinc@nvidia.com>
Link: https://lore.kernel.org/linux-iommu/arG6hmng3NddGEHm@nvidia.com/
Assisted-by: LLM
Signed-off-by: Peng Fan <peng.fan@nxp.com>
---
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 92 ++++++++++++++++++++---------
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h |  3 +
 2 files changed, 66 insertions(+), 29 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 69c2c3596b06a..d306e4af90ef0 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -2044,8 +2044,8 @@ static int arm_smmu_streams_cmp_node(struct rb_node *lhs,
 		&rb_entry(lhs, struct arm_smmu_stream, node)->id, rhs);
 }
 
-static struct arm_smmu_master *
-arm_smmu_find_master(struct arm_smmu_device *smmu, u32 sid)
+static struct arm_smmu_stream *
+arm_smmu_find_stream(struct arm_smmu_device *smmu, u32 sid)
 {
 	struct rb_node *node;
 
@@ -2054,7 +2054,20 @@ arm_smmu_find_master(struct arm_smmu_device *smmu, u32 sid)
 	node = rb_find(&sid, &smmu->streams, arm_smmu_streams_cmp_key);
 	if (!node)
 		return NULL;
-	return rb_entry(node, struct arm_smmu_stream, node)->master;
+	return rb_entry(node, struct arm_smmu_stream, node);
+}
+
+static struct arm_smmu_master *
+arm_smmu_find_master(struct arm_smmu_device *smmu, u32 sid)
+{
+	struct arm_smmu_stream *stream;
+
+	stream = arm_smmu_find_stream(smmu, sid);
+	if (!stream)
+		return NULL;
+	if (!list_empty(&stream->shared_masters))
+		return NULL;
+	return stream->master;
 }
 
 /* IRQ and event handlers */
@@ -4109,36 +4122,41 @@ static int arm_smmu_insert_master(struct arm_smmu_device *smmu,
 		kfree(master->streams);
 		return -ENOMEM;
 	}
+	INIT_LIST_HEAD(&master->shared_masters_elm);
 
 	mutex_lock(&smmu->streams_mutex);
 	for (i = 0; i < fwspec->num_ids; i++) {
 		struct arm_smmu_stream *stream;
-		struct rb_node *existing;
 		u32 sid = fwspec->ids[i];
 
 		ret = arm_smmu_init_sid_strtab(smmu, sid);
 		if (ret)
 			break;
 
-		existing = rb_find(&sid, &smmu->streams,
-				   arm_smmu_streams_cmp_key);
-		if (existing) {
-			struct arm_smmu_master *existing_master =
-				rb_entry(existing, struct arm_smmu_stream, node)
-					->master;
-
+		stream = arm_smmu_find_stream(smmu, sid);
+		if (stream) {
 			/* Bridged PCI devices may end up with duplicated IDs */
-			if (existing_master == master) {
-				master->streams[i] = rb_entry(existing,
-					struct arm_smmu_stream, node);
+			if (stream->master == master) {
+				master->streams[i] = stream;
 				continue;
 			}
 
-			dev_warn(master->dev,
-				 "Aliasing StreamID 0x%x (from %s) unsupported, expect DMA to be broken\n",
-				 sid, dev_name(existing_master->dev));
-			ret = -ENODEV;
-			break;
+			if (master->num_streams != 1 ||
+			    stream->master->num_streams != 1) {
+				dev_warn(master->dev,
+					 "Shared StreamID 0x%x not supported for multi-SID masters\n",
+					 sid);
+				ret = -ENODEV;
+				break;
+			}
+
+			if (list_empty(&stream->shared_masters))
+				list_add_tail(&stream->master->shared_masters_elm,
+					      &stream->shared_masters);
+			list_add_tail(&master->shared_masters_elm,
+				      &stream->shared_masters);
+			master->streams[i] = stream;
+			continue;
 		}
 
 		stream = kzalloc_obj(*stream, GFP_KERNEL);
@@ -4148,6 +4166,7 @@ static int arm_smmu_insert_master(struct arm_smmu_device *smmu,
 		}
 		stream->id = sid;
 		stream->master = master;
+		INIT_LIST_HEAD(&stream->shared_masters);
 
 		rb_find_add(&stream->node, &smmu->streams,
 			    arm_smmu_streams_cmp_node);
@@ -4155,6 +4174,7 @@ static int arm_smmu_insert_master(struct arm_smmu_device *smmu,
 	}
 
 	if (ret) {
+		list_del_init(&master->shared_masters_elm);
 		for (i--; i >= 0; i--) {
 			int j;
 
@@ -4193,17 +4213,31 @@ static void arm_smmu_remove_master(struct arm_smmu_master *master)
 		return;
 
 	mutex_lock(&smmu->streams_mutex);
-	for (i = 0; i < master->num_streams; i++) {
-		int j;
+	if (!list_empty(&master->shared_masters_elm)) {
+		struct arm_smmu_stream *stream = master->streams[0];
 
-		/* Skip duplicated SID pointers already freed */
-		for (j = 0; j < i; j++)
-			if (master->streams[j] == master->streams[i])
-				break;
-		if (j < i)
-			continue;
-		rb_erase(&master->streams[i]->node, &smmu->streams);
-		kfree(master->streams[i]);
+		list_del_init(&master->shared_masters_elm);
+		if (list_is_singular(&stream->shared_masters)) {
+			struct arm_smmu_master *last;
+
+			last = list_first_entry(&stream->shared_masters,
+					struct arm_smmu_master,
+					shared_masters_elm);
+			list_del_init(&last->shared_masters_elm);
+		}
+	} else {
+		for (i = 0; i < master->num_streams; i++) {
+			int j;
+
+			/* Skip duplicated SID pointers already freed */
+			for (j = 0; j < i; j++)
+				if (master->streams[j] == master->streams[i])
+					break;
+			if (j < i)
+				continue;
+			rb_erase(&master->streams[i]->node, &smmu->streams);
+			kfree(master->streams[i]);
+		}
 	}
 	mutex_unlock(&smmu->streams_mutex);
 
diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
index ba430078cbce9..2ed7a66c8b0b8 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
@@ -969,6 +969,8 @@ struct arm_smmu_stream {
 	u32				id;
 	struct arm_smmu_master		*master;
 	struct rb_node			node;
+	bool				ste_installed;
+	struct list_head		shared_masters;
 };
 
 struct arm_smmu_vmaster {
@@ -1017,6 +1019,7 @@ struct arm_smmu_master {
 	bool				ste_ats_enabled : 1;
 	bool				stall_enabled;
 	bool				ats_always_on;
+	struct list_head		shared_masters_elm;
 	unsigned int			ssid_bits;
 	unsigned int			iopf_refcount;
 };

-- 
2.34.1