[PATCH v8 15/21] cxl/region/extent: Expose region extent information in sysfs

[Ira Weiny <ira.weiny@xxxxxxxxx>]

Extent information can be helpful to the user to coordinate memory usage
with the external orchestrator and FM.

Expose the details of region extents by creating the following
sysfs entries.

        /sys/bus/cxl/devices/dax_regionX/extentX.Y
        /sys/bus/cxl/devices/dax_regionX/extentX.Y/offset
        /sys/bus/cxl/devices/dax_regionX/extentX.Y/length
        /sys/bus/cxl/devices/dax_regionX/extentX.Y/tag

Based on an original patch by Navneet Singh.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
Reviewed-by: Fan Ni <fan.ni@xxxxxxxxxxx>
Tested-by: Fan Ni <fan.ni@xxxxxxxxxxx>
Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>
---
 Documentation/ABI/testing/sysfs-bus-cxl | 33 +++++++++++++++++++
 drivers/cxl/core/extent.c               | 58 +++++++++++++++++++++++++++++++++
 2 files changed, 91 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-bus-cxl b/Documentation/ABI/testing/sysfs-bus-cxl
index aeff248ea368cf49c9977fcaf43ab4def978e896..ee2ef4ea33e17cbc65e1252753f46f6d0dce1aee 100644
--- a/Documentation/ABI/testing/sysfs-bus-cxl
+++ b/Documentation/ABI/testing/sysfs-bus-cxl
@@ -632,3 +632,36 @@ Description:
 		See Documentation/ABI/stable/sysfs-devices-node. access0 provides
 		the number to the closest initiator and access1 provides the
 		number to the closest CPU.
+
+What:		/sys/bus/cxl/devices/dax_regionX/extentX.Y/offset
+Date:		December, 2024
+KernelVersion:	v6.13
+Contact:	linux-cxl@xxxxxxxxxxxxxxx
+Description:
+		(RO) [For Dynamic Capacity regions only] Users can use the
+		extent information to create DAX devices on specific extents.
+		This is done by creating and destroying DAX devices in specific
+		sequences and looking at the mappings created.  Extent offset
+		within the region.
+
+What:		/sys/bus/cxl/devices/dax_regionX/extentX.Y/length
+Date:		December, 2024
+KernelVersion:	v6.13
+Contact:	linux-cxl@xxxxxxxxxxxxxxx
+Description:
+		(RO) [For Dynamic Capacity regions only] Users can use the
+		extent information to create DAX devices on specific extents.
+		This is done by creating and destroying DAX devices in specific
+		sequences and looking at the mappings created.  Extent length
+		within the region.
+
+What:		/sys/bus/cxl/devices/dax_regionX/extentX.Y/tag
+Date:		December, 2024
+KernelVersion:	v6.13
+Contact:	linux-cxl@xxxxxxxxxxxxxxx
+Description:
+		(RO) [For Dynamic Capacity regions only] Users can use the
+		extent information to create DAX devices on specific extents.
+		This is done by creating and destroying DAX devices in specific
+		sequences and looking at the mappings created.  UUID extent
+		tag.
diff --git a/drivers/cxl/core/extent.c b/drivers/cxl/core/extent.c
index a45ff84727b0f8c2567f0d2dd8b5c261b23695e3..0ebdbe983d094de89579527459cd75e3e7e2b6c7 100644
--- a/drivers/cxl/core/extent.c
+++ b/drivers/cxl/core/extent.c
@@ -6,6 +6,63 @@
 
 #include "core.h"
 
+static ssize_t offset_show(struct device *dev, struct device_attribute *attr,
+			   char *buf)
+{
+	struct region_extent *region_extent = to_region_extent(dev);
+
+	return sysfs_emit(buf, "%#llx\n", region_extent->hpa_range.start);
+}
+static DEVICE_ATTR_RO(offset);
+
+static ssize_t length_show(struct device *dev, struct device_attribute *attr,
+			   char *buf)
+{
+	struct region_extent *region_extent = to_region_extent(dev);
+	u64 length = range_len(&region_extent->hpa_range);
+
+	return sysfs_emit(buf, "%#llx\n", length);
+}
+static DEVICE_ATTR_RO(length);
+
+static ssize_t tag_show(struct device *dev, struct device_attribute *attr,
+			char *buf)
+{
+	struct region_extent *region_extent = to_region_extent(dev);
+
+	return sysfs_emit(buf, "%pUb\n", &region_extent->tag);
+}
+static DEVICE_ATTR_RO(tag);
+
+static struct attribute *region_extent_attrs[] = {
+	&dev_attr_offset.attr,
+	&dev_attr_length.attr,
+	&dev_attr_tag.attr,
+	NULL
+};
+
+static uuid_t empty_tag = { 0 };
+
+static umode_t region_extent_visible(struct kobject *kobj,
+				     struct attribute *a, int n)
+{
+	struct device *dev = kobj_to_dev(kobj);
+	struct region_extent *region_extent = to_region_extent(dev);
+
+	if (a == &dev_attr_tag.attr &&
+	    uuid_equal(&region_extent->tag, &empty_tag))
+		return 0;
+
+	return a->mode;
+}
+
+static const struct attribute_group region_extent_attribute_group = {
+	.attrs = region_extent_attrs,
+	.is_visible = region_extent_visible,
+};
+
+__ATTRIBUTE_GROUPS(region_extent_attribute);
+
 static void cxled_release_extent(struct cxl_endpoint_decoder *cxled,
 				 struct cxled_extent *ed_extent)
 {
@@ -44,6 +101,7 @@ static void region_extent_release(struct device *dev)
 static const struct device_type region_extent_type = {
 	.name = "extent",
 	.release = region_extent_release,
+	.groups = region_extent_attribute_groups,
 };
 
 bool is_region_extent(struct device *dev)

-- 
2.47.1