Re: [PATCH v3 6/7] hw/arm/smmuv3: Set default ats, ril, ssidsize, oas to auto

[Nathan Chen]

On 5/19/2026 8:59 AM, Eric Auger wrote:

On 5/12/26 9:35 PM, Nathan Chen wrote:
From: Nathan Chen<nath...@nvidia.com>

Set the default value of ATS, RIL, SSIDSIZE, and OAS to auto, in order
to match the host IOMMU properties when accel=on.

If accel=off and these property values are set to auto, the default
property values defined in smmuv3_init_id_regs() for OAS and RIL will
remain unchanged, while SSIDSIZE and ATS values will remain initialized
at 0.

Introduce a new compat for the changed defaults.

Signed-off-by: Nathan Chen<nath...@nvidia.com>
---
  hw/arm/smmuv3.c   | 23 +++++++++++++++--------
  hw/core/machine.c |  5 +++++
  2 files changed, 20 insertions(+), 8 deletions(-)

diff --git a/hw/arm/smmuv3.c b/hw/arm/smmuv3.c
index 31c2eec2f4..665e6a2538 100644
--- a/hw/arm/smmuv3.c
+++ b/hw/arm/smmuv3.c
@@ -2129,12 +2129,19 @@ static const Property smmuv3_properties[] = {
      DEFINE_PROP_BOOL("accel", SMMUv3State, accel, false),
      /* GPA of MSI doorbell, for SMMUv3 accel use. */
      DEFINE_PROP_UINT64("msi-gpa", SMMUv3State, msi_gpa, 0),
+    /*
+     * AUTO values for accel=off will resolve to:
+     * ril: on
+     * ats: off
+     * oas: 44
+     * ssidsize: 0
+     */
      /* RIL can be turned off for accel cases */
-    DEFINE_PROP_ON_OFF_AUTO("ril", SMMUv3State, ril, ON_OFF_AUTO_ON),
-    DEFINE_PROP_ON_OFF_AUTO("ats", SMMUv3State, ats, ON_OFF_AUTO_OFF),
-    DEFINE_PROP_OAS_MODE("oas", SMMUv3State, oas, OAS_MODE_44),
+    DEFINE_PROP_ON_OFF_AUTO("ril", SMMUv3State, ril, ON_OFF_AUTO_AUTO),
+    DEFINE_PROP_ON_OFF_AUTO("ats", SMMUv3State, ats, ON_OFF_AUTO_AUTO),
+    DEFINE_PROP_OAS_MODE("oas", SMMUv3State, oas, OAS_MODE_AUTO),
      DEFINE_PROP_SSIDSIZE_MODE("ssidsize", SMMUv3State, ssidsize,
-                              SSID_SIZE_MODE_0),
+                              SSID_SIZE_MODE_AUTO),
  };
  
  static void smmuv3_instance_init(Object *obj)
@@ -2162,20 +2169,20 @@ static void smmuv3_class_init(ObjectClass *klass, const 
void *data)
          "configured in nested mode for vfio-pci dev assignment");
      object_class_property_set_description(klass, "ril",
          "Enable/disable range invalidation support (for accel=on). "
-        "Valid values are on, off, and auto. Defaults to on. "
+        "Valid values are on, off, and auto. Defaults to auto. "
          "Any attempt to turn it 'on' while the host does not support "
          "it would fail.");
      object_class_property_set_description(klass, "ats",
          "Enable/disable ATS support (for accel=on). "
-        "Valid values are on, off, and auto. Defaults to off. "
+        "Valid values are on, off, and auto. Defaults to auto. "
          "Please ensure host platform supports ATS before setting it "
          "to on.");
      object_class_property_set_description(klass, "oas",
          "Set Output Address Size in bits (for accel=on). "
-        "Valid values are 44, 48, and auto. Defaults to 44 bits.");
+        "Valid values are 44, 48, and auto. Defaults to auto.");
not really related to this patch but I notice that we do not have any
"Please ensure host platform supports..." statement as opposed to
previous props.
While some host requirements are needed to be statistied too.

smmuv3-accel.c:    if (FIELD_EX32(info->idr[5], IDR5, OAS) <
smmuv3-accel.c:                FIELD_EX32(s->idr[5], IDR5, OAS)) {

      object_class_property_set_description(klass, "ssidsize",
          "Set number of bits used to represent SubstreamIDs (SSIDs). "
-        "Valid values are 0-20 and auto. Defaults to 0. "
+        "Valid values are 0-20 and auto. Defaults to auto. "
          "A value of N allows SSIDs in the range [0 .. 2^N - 1]. "
          "A value of 0 disables SubstreamID support. A value greater "
          "than 0 is required to enable PASID support.");
same here.

Got it, I will update with host requirement guidance for OAS and 
SSIDSIZE on the next refresh.

smmuv3-accel.c:        s->idr[1] = FIELD_DP32(s->idr[1], IDR1, SSIDSIZE,
smmuv3-accel.c:                               FIELD_EX32(info->idr[1],
IDR1, SSIDSIZE));

Also it is not written (for accel=on)
I can reword the accel section to something like:
"Enable SMMUv3 accelerator support. Allows host SMMUv3 to be configured 
in nested mode for vfio-pci dev assignment. Please ensure the host 
SMMUv3 supports hardware-accelerated VFIO-PCI device assignment before 
enabling."

Should I create a new patch for this update to the accel guidance or 
consolidate into the next refresh of this current patch?

Thanks,
Nathan

diff --git a/hw/core/machine.c b/hw/core/machine.c
index 63baff859f..3339da99ee 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -38,9 +38,14 @@
  #include "hw/virtio/virtio-iommu.h"
  #include "hw/acpi/generic_event_device.h"
  #include "qemu/audio.h"
+#include "hw/arm/smmuv3.h"
  
  GlobalProperty hw_compat_11_0[] = {
      { "chardev-vc", "encoding", "cp437" },
+    { TYPE_ARM_SMMUV3, "ats", "off" },
+    { TYPE_ARM_SMMUV3, "ril", "on" },
+    { TYPE_ARM_SMMUV3, "ssidsize", "0" },
+    { TYPE_ARM_SMMUV3, "oas", "44" },
  };
  const size_t hw_compat_11_0_len = G_N_ELEMENTS(hw_compat_11_0);