[PATCH v2] driver core: platform: expose numa_node to users in sysfs

[Barry Song]

For some platform devices like iommu, particually ARM smmu, users may
care about the numa locality. for example, if threads and drivers run
near iommu, they may get much better performance on dma_unmap_sg.
For other platform devices, users may still want to know the hardware
topology.

Cc: Prime Zeng <prime.zeng@xxxxxxxxxxxxx>
Cc: Robin Murphy <robin.murphy@xxxxxxx>
Signed-off-by: Barry Song <song.bao.hua@xxxxxxxxxxxxx>
---
 -v2: add the numa_node entry in Documentation/ABI/

 Documentation/ABI/testing/sysfs-bus-platform | 10 ++++++++
 drivers/base/platform.c                      | 26 +++++++++++++++++++-
 2 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/Documentation/ABI/testing/sysfs-bus-platform b/Documentation/ABI/testing/sysfs-bus-platform
index 5172a6124b27..e8f5958c1d18 100644
--- a/Documentation/ABI/testing/sysfs-bus-platform
+++ b/Documentation/ABI/testing/sysfs-bus-platform
@@ -18,3 +18,13 @@ Description:
 		devices to opt-out of driver binding using a driver_override
 		name such as "none".  Only a single driver may be specified in
 		the override, there is no support for parsing delimiters.
+
+What:		/sys/bus/platform/devices/.../numa_node
+Date:		June 2020
+Contact:	Barry Song <song.bao.hua@xxxxxxxxxxxxx>
+Description:
+		This file contains the NUMA node to which the platform device
+		is attached. It won't be visible if the node is unknown. The
+		value comes from an ACPI _PXM method or a similar firmware
+		source. Initial users for this file would be devices like
+		arm smmu which are populated by arm64 acpi_iort.
diff --git a/drivers/base/platform.c b/drivers/base/platform.c
index b27d0f6c18c9..7794b9a38d82 100644
--- a/drivers/base/platform.c
+++ b/drivers/base/platform.c
@@ -1062,13 +1062,37 @@ static ssize_t driver_override_show(struct device *dev,
 }
 static DEVICE_ATTR_RW(driver_override);
 
+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 platform_dev_attrs_visible(struct kobject *kobj, struct attribute *a,
+		int n)
+{
+	struct device *dev = container_of(kobj, typeof(*dev), kobj);
+
+	if (a == &dev_attr_numa_node.attr &&
+			dev_to_node(dev) == NUMA_NO_NODE)
+		return 0;
+
+	return a->mode;
+}
 
 static struct attribute *platform_dev_attrs[] = {
 	&dev_attr_modalias.attr,
+	&dev_attr_numa_node.attr,
 	&dev_attr_driver_override.attr,
 	NULL,
 };
-ATTRIBUTE_GROUPS(platform_dev);
+
+static struct attribute_group platform_dev_group = {
+	.attrs = platform_dev_attrs,
+	.is_visible = platform_dev_attrs_visible,
+};
+__ATTRIBUTE_GROUPS(platform_dev);
 
 static int platform_uevent(struct device *dev, struct kobj_uevent_env *env)
 {
-- 
2.23.0