[PATCH RFC v3 1/3] iommu/arm-smmu-v3: Support shared SIDs in insert/remove_master
Peng Fan (OSS)
peng.fan at oss.nxp.com
Wed Sep 30 04:25:01 PDT 2026
From: Peng Fan <peng.fan at nxp.com>
Some SoCs have a limited number of IOMMU Stream IDs and hardware
that inherently shares them. For example, the NXP i.MX95 has only
64 SIDs (6-bit internal bus) serving 64+ DMA initiators across
separate IP blocks - MMC, SD, NET, PCI, DMA, NPU, DSP, DISPLAY
and more. Genuinely distinct platform devices share a SID by
hardware design because the SID space is exhausted.
When arm_smmu_insert_master() encounters a SID already owned by a
different single-SID master, instead of failing with -ENODEV, link
the new master into the existing stream's shared_masters list.
The stream structure is shared directly: the RB tree entry remains
the same, and all sharing masters are tracked via list_head.
On removal, if the departing master owns the canonical stream,
transfer ownership to the next sharer.
Sharing is restricted to single-SID masters (num_streams == 1)
since multi-SID sharing would require more complex tracking.
Signed-off-by: Peng Fan <peng.fan at nxp.com>
---
drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 76 +++++++++++++++++++++++------
drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h | 9 ++++
2 files changed, 70 insertions(+), 15 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 5732f3ba0122d..940f34465c0fa 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 */
@@ -4115,7 +4128,10 @@ static int arm_smmu_insert_master(struct arm_smmu_device *smmu,
new_stream->id = fwspec->ids[i];
new_stream->master = master;
+ new_stream->ste_installed = false;
+ INIT_LIST_HEAD(&new_stream->shared_masters);
}
+ INIT_LIST_HEAD(&master->shared_masters_elm);
/* Put the ids into order for sorted to_merge/to_unref arrays */
sort(master->streams, master->num_streams,
@@ -4136,23 +4152,29 @@ static int arm_smmu_insert_master(struct arm_smmu_device *smmu,
existing = rb_find_add(&new_stream->node, &smmu->streams,
arm_smmu_streams_cmp_node);
if (existing) {
- struct arm_smmu_master *existing_master =
- rb_entry(existing, struct arm_smmu_stream, node)
- ->master;
+ struct arm_smmu_stream *existing_stream =
+ rb_entry(existing, struct arm_smmu_stream, node);
/* Bridged PCI devices may end up with duplicated IDs */
- if (existing_master == master)
+ if (existing_stream->master == master)
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) {
+ dev_warn(master->dev,
+ "Shared StreamID 0x%x not supported for multi-SID masters\n",
+ sid);
+ ret = -ENODEV;
+ break;
+ }
+
+ list_add_tail(&master->shared_masters_elm,
+ &existing_stream->shared_masters);
+ continue;
}
}
if (ret) {
+ list_del_init(&master->shared_masters_elm);
for (i--; i >= 0; i--)
rb_erase(&master->streams[i].node, &smmu->streams);
kfree(master->streams);
@@ -4167,14 +4189,38 @@ static void arm_smmu_remove_master(struct arm_smmu_master *master)
{
int i;
struct arm_smmu_device *smmu = master->smmu;
- struct iommu_fwspec *fwspec = dev_iommu_fwspec_get(master->dev);
if (!smmu || !master->streams)
return;
mutex_lock(&smmu->streams_mutex);
- for (i = 0; i < fwspec->num_ids; i++)
- rb_erase(&master->streams[i].node, &smmu->streams);
+ list_del_init(&master->shared_masters_elm);
+ for (i = 0; i < master->num_streams; i++) {
+ u32 sid = master->streams[i].id;
+ struct arm_smmu_stream *stream;
+
+ if (i > 0 && master->streams[i - 1].id == sid)
+ continue;
+
+ stream = arm_smmu_find_stream(smmu, sid);
+ if (!stream)
+ continue;
+
+ if (stream->master != master)
+ continue;
+
+ if (list_empty(&stream->shared_masters)) {
+ rb_erase(&stream->node, &smmu->streams);
+ } else {
+ struct arm_smmu_master *next;
+
+ next = list_first_entry(&stream->shared_masters,
+ struct arm_smmu_master,
+ shared_masters_elm);
+ list_del_init(&next->shared_masters_elm);
+ stream->master = next;
+ }
+ }
mutex_unlock(&smmu->streams_mutex);
kfree(master->streams);
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 dd2fee2f560e6..ea0aa345fb673 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 +969,10 @@ struct arm_smmu_stream {
u32 id;
struct arm_smmu_master *master;
struct rb_node node;
+ /* Set when the STE has been programmed for this stream. */
+ bool ste_installed;
+ /* List of masters sharing this SID. Empty unless shared. */
+ struct list_head shared_masters;
};
struct arm_smmu_vmaster {
@@ -1017,6 +1021,11 @@ struct arm_smmu_master {
bool ste_ats_enabled : 1;
bool stall_enabled;
bool ats_always_on;
+ /*
+ * Links into arm_smmu_stream.shared_masters. Supports num_streams == 1
+ * only. Empty if SID is not shared.
+ */
+ struct list_head shared_masters_elm;
unsigned int ssid_bits;
unsigned int iopf_refcount;
};
--
2.34.1
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