Re: [RFC PATCH 2/8] hw/arm/smmuv3-accel: Introduce _AUTO support for ATS

[Nathan Chen]

On 3/11/2026 11:10 AM, Eric Auger wrote:
On 3/9/26 8:21 PM, Nathan Chen wrote:
From: Nathan Chen<nath...@nvidia.com>

Allow accelerated SMMUv3 Address Translation Services support property
to be derived from host IOMMU capabilities. Derive host values using
IOMMU_GET_HW_INFO, retrieving ATS capability from IDR0.

Set the default value of ATS to auto. The default for ATS support used
to be set to off, but we change it to match what the host IOMMU
properties report.

Add a "ats-enabled" read-only property for smmuv3 to address an
expected bool for the "ats" property in iort_smmuv3_devices().

Signed-off-by: Nathan Chen<nath...@nvidia.com>
---
  hw/arm/smmuv3-accel.c    | 25 +++++++++++++++++++++++--
  hw/arm/smmuv3.c          | 12 ++++++++++--
  hw/arm/virt-acpi-build.c |  2 +-
  include/hw/arm/smmuv3.h  |  2 +-
  4 files changed, 35 insertions(+), 6 deletions(-)

diff --git a/hw/arm/smmuv3-accel.c b/hw/arm/smmuv3-accel.c
index 617629bacd..8fec335557 100644
--- a/hw/arm/smmuv3-accel.c
+++ b/hw/arm/smmuv3-accel.c
@@ -52,6 +52,12 @@ static void smmuv3_accel_auto_finalise(SMMUv3State *s, 
PCIDevice *pdev,
          return;
      }
  
+    /* Update ATS if auto from info */
+    if (s->ats == ON_OFF_AUTO_AUTO) {
+        s->idr[0] = FIELD_DP32(s->idr[0], IDR0, ATS,
+                               FIELD_EX32(info->idr[0], IDR0, ATS));
+    }
+
      accel->auto_finalised = true;
  }
  
@@ -124,6 +130,13 @@ smmuv3_accel_check_hw_compatible(SMMUv3State *s,
                     smmuv3_oas_bits(FIELD_EX32(s->idr[5], IDR5, OAS)));
          return false;
      }
+    /* Check ATS value opted is compatible with Host SMMUv3 */
+    if (FIELD_EX32(info->idr[0], IDR0, ATS) <
+                FIELD_EX32(s->idr[0], IDR0, ATS)) {
+        error_setg(errp, "Host SMMUv3 doesn't support Address Translation"
+                   " Services");
+        return false;
+    }
Shouldn't this chunk be a separate fix for previous accel SMMU series?

Yes, I'll separate this out to be a separate commit in the next refresh.

  
      /* QEMU SMMUv3 supports GRAN4K/GRAN16K/GRAN64K translation granules */
      if (FIELD_EX32(info->idr[5], IDR5, GRAN4K) !=
@@ -844,8 +857,12 @@ void smmuv3_accel_idr_override(SMMUv3State *s)
      /* By default QEMU SMMUv3 has RIL. Update IDR3 if user has disabled it */
      s->idr[3] = FIELD_DP32(s->idr[3], IDR3, RIL, s->ril);
  
-    /* QEMU SMMUv3 has no ATS. Advertise ATS if opt-in by property */
-    s->idr[0] = FIELD_DP32(s->idr[0], IDR0, ATS, s->ats);
+    /* Only override ATS if user explicitly set ON or OFF */
+    if (s->ats == ON_OFF_AUTO_ON) {
+        s->idr[0] = FIELD_DP32(s->idr[0], IDR0, ATS, 1);
+    } else if (s->ats == ON_OFF_AUTO_OFF) {
+        s->idr[0] = FIELD_DP32(s->idr[0], IDR0, ATS, 0);
+    }
  
      /* Advertise 48-bit OAS in IDR5 when requested (default is 44 bits). */
      if (s->oas == SMMU_OAS_48BIT) {
@@ -923,4 +940,8 @@ void smmuv3_accel_init(SMMUv3State *s)
      s->s_accel = g_new0(SMMUv3AccelState, 1);
      bs->iommu_ops = &smmuv3_accel_ops;
      smmuv3_accel_as_init(s);
+
+    if (s->ats == ON_OFF_AUTO_AUTO) {
+        s->s_accel->auto_mode = true;
+    }
  }
diff --git a/hw/arm/smmuv3.c b/hw/arm/smmuv3.c
index 068108e49b..197ba7c77b 100644
--- a/hw/arm/smmuv3.c
+++ b/hw/arm/smmuv3.c
@@ -317,6 +317,12 @@ static void smmuv3_init_id_regs(SMMUv3State *s)
      smmuv3_accel_idr_override(s);
  }
  
+static bool get_ats_enabled(Object *obj, Error **errp)
+{
+    SMMUv3State *s = ARM_SMMUV3(obj);
+    return FIELD_EX32(s->idr[0], IDR0, ATS);
+}
+
  static void smmuv3_reset(SMMUv3State *s)
  {
      s->cmdq.base = deposit64(s->cmdq.base, 0, 5, SMMU_CMDQS);
@@ -1971,7 +1977,7 @@ static bool smmu_validate_property(SMMUv3State *s, Error 
**errp)
              error_setg(errp, "ril can only be disabled if accel=on");
              return false;
          }
-        if (s->ats) {
+        if (s->ats == ON_OFF_AUTO_ON) {
              error_setg(errp, "ats can only be enabled if accel=on");
              return false;
          }
@@ -2128,7 +2134,7 @@ static const Property smmuv3_properties[] = {
      DEFINE_PROP_UINT64("msi-gpa", SMMUv3State, msi_gpa, 0),
      /* RIL can be turned off for accel cases */
      DEFINE_PROP_BOOL("ril", SMMUv3State, ril, true),
-    DEFINE_PROP_BOOL("ats", SMMUv3State, ats, false),
+    DEFINE_PROP_ON_OFF_AUTO("ats", SMMUv3State, ats, ON_OFF_AUTO_AUTO),
      DEFINE_PROP_UINT8("oas", SMMUv3State, oas, 44),
      DEFINE_PROP_UINT8("ssidsize", SMMUv3State, ssidsize, 0),
  };
@@ -2153,6 +2159,8 @@ static void smmuv3_class_init(ObjectClass *klass, const 
void *data)
      dc->hotpluggable = false;
      dc->user_creatable = true;
  
+    object_class_property_add_bool(klass, "ats-enabled", get_ats_enabled, NULL);
+
      object_class_property_set_description(klass, "accel",
          "Enable SMMUv3 accelerator support. Allows host SMMUv3 to be "
          "configured in nested mode for vfio-pci dev assignment");
diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c
index 719d2f994e..6c77fc5f6a 100644
--- a/hw/arm/virt-acpi-build.c
+++ b/hw/arm/virt-acpi-build.c
@@ -402,7 +402,7 @@ static int iort_smmuv3_devices(Object *obj, void *opaque)
  
      bus = PCI_BUS(object_property_get_link(obj, "primary-bus", &error_abort));
      sdev.accel = object_property_get_bool(obj, "accel", &error_abort);
-    sdev.ats = object_property_get_bool(obj, "ats", &error_abort);
+    sdev.ats = object_property_get_bool(obj, "ats-enabled", &error_abort);
are we obliged to use a prop here.
we can dynamic cast to the TYPE_ARM_SMMUV3 and use an exported helper, no?

I'll look into replacing this ats-enabled prop with a helper that 
accepts the dynamic casted TYPE_ARM_SMMUV3 object and determines whether 
ATS support is being advertised.

Thanks,
Nathan