[PATCH] iommu/arm-smmu-v3: expose numa_node attribute to users in sysfs

[Barry Song]

As tests show the latency of dma_unmap can increase dramatically while
calling them cross NUMA nodes, especially cross CPU packages, eg.
300ns vs 800ns while waiting for the completion of CMD_SYNC in an
empty command queue. The large latency causing by remote node will
in turn make contention of the command queue more serious, and enlarge
the latency of DMA users within local NUMA nodes.

Users might intend to enforce NUMA locality with the consideration of
the position of SMMU. The patch provides minor benefit by presenting
this information to users directly, as they might want to know it without
checking hardware spec at all.

Signed-off-by: Barry Song <song.bao.hua at hisilicon.com>
---
 drivers/iommu/arm-smmu-v3.c | 40 ++++++++++++++++++++++++++++++++++++-
 1 file changed, 39 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index 82508730feb7..754c4d59498b 100644
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -4021,6 +4021,44 @@ err_reset_pci_ops: __maybe_unused;
 	return err;
 }
 
+static ssize_t numa_node_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%d\n", dev_to_node(dev));
+}
+static DEVICE_ATTR_RO(numa_node);
+
+static umode_t arm_smmu_numa_attr_visible(struct kobject *kobj, struct attribute *a,
+		int n)
+{
+	struct device *dev = container_of(kobj, typeof(*dev), kobj);
+
+	if (!IS_ENABLED(CONFIG_NUMA))
+		return 0;
+
+	if (a == &dev_attr_numa_node.attr &&
+			dev_to_node(dev) == NUMA_NO_NODE)
+		return 0;
+
+	return a->mode;
+}
+
+static struct attribute *arm_smmu_dev_attrs[] = {
+	&dev_attr_numa_node.attr,
+	NULL
+};
+
+static struct attribute_group arm_smmu_dev_attrs_group = {
+	.attrs          = arm_smmu_dev_attrs,
+	.is_visible     = arm_smmu_numa_attr_visible,
+};
+
+
+static const struct attribute_group *arm_smmu_dev_attrs_groups[] = {
+	&arm_smmu_dev_attrs_group,
+	NULL,
+};
+
 static int arm_smmu_device_probe(struct platform_device *pdev)
 {
 	int irq, ret;
@@ -4097,7 +4135,7 @@ static int arm_smmu_device_probe(struct platform_device *pdev)
 		return ret;
 
 	/* And we're up. Go go go! */
-	ret = iommu_device_sysfs_add(&smmu->iommu, dev, NULL,
+	ret = iommu_device_sysfs_add(&smmu->iommu, dev, arm_smmu_dev_attrs_groups,
 				     "smmu3.%pa", &ioaddr);
 	if (ret)
 		return ret;
-- 
2.23.0