[PATCH 3 22/23] cxl: Export sysfs attributes for memory device QTG ID

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Export qtg_id sysfs attributes for the CXL memory device. The QTG ID
should show up as /sys/bus/cxl/devices/memX/ram/qtg_id for the volatile
partition and /sys/bus/cxl/devices/memX/pmem/qtg_id for the persistent
partition. The QTG ID is retrieved via _DSM after supplying the
calculated bandwidth and latency for the entire CXL path from device to
the CPU. This ID is used to match up to the root decoder QTG ID to
determine which CFMWS the memory range of a hotplugged CXL mem device
should be assigned under.

While there may be multiple DSMAS exported by the device CDAT, the driver
will only expose the first QTG ID per partition in sysfs for now. In the
future when multiple QTG IDs are necessary, they can be exposed. [1]

[1]: https://lore.kernel.org/linux-cxl/167571650007.587790.10040913293130712882.stgit@djiang5-mobl3.local/T/#md2a47b1ead3e1ba08f50eab29a4af1aed1d215ab

Suggested-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Signed-off-by: Dave Jiang <dave.jiang@xxxxxxxxx>

---
v3:
- Expand description of qtg_id. (Alison)
---
 Documentation/ABI/testing/sysfs-bus-cxl |   22 ++++++++++++++++++++++
 drivers/cxl/core/memdev.c               |   26 ++++++++++++++++++++++++++
 2 files changed, 48 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-bus-cxl b/Documentation/ABI/testing/sysfs-bus-cxl
index 471ac9a37078..1640b6ff5429 100644
--- a/Documentation/ABI/testing/sysfs-bus-cxl
+++ b/Documentation/ABI/testing/sysfs-bus-cxl
@@ -28,6 +28,17 @@ Description:
 		Payload in the CXL-2.0 specification.
 
 
+What:		/sys/bus/cxl/devices/memX/ram/qtg_id
+Date:		January, 2023
+KernelVersion:	v6.4
+Contact:	linux-cxl@xxxxxxxxxxxxxxx
+Description:
+		(RO) Shows calculated QoS Throttling Group ID for the
+		"Volatile Only Capacity" DPA range. When creating regions,
+		the qtg_id for the memory range should match the root
+		decoder's qtg_id to have optimal performance.
+
+
 What:		/sys/bus/cxl/devices/memX/pmem/size
 Date:		December, 2020
 KernelVersion:	v5.12
@@ -38,6 +49,17 @@ Description:
 		Payload in the CXL-2.0 specification.
 
 
+What:		/sys/bus/cxl/devices/memX/pmem/qtg_id
+Date:		January, 2023
+KernelVersion:	v6.4
+Contact:	linux-cxl@xxxxxxxxxxxxxxx
+Description:
+		(RO) Shows calculated QoS Throttling Group ID for the
+		"Persistent Only Capacity" DPA range. When creating regions,
+		the qtg_id for the memory range should match the root
+		decoder's qtg_id to have optimal performance.
+
+
 What:		/sys/bus/cxl/devices/memX/serial
 Date:		January, 2022
 KernelVersion:	v5.18
diff --git a/drivers/cxl/core/memdev.c b/drivers/cxl/core/memdev.c
index 28a05f2fe32d..04058ec5fcff 100644
--- a/drivers/cxl/core/memdev.c
+++ b/drivers/cxl/core/memdev.c
@@ -76,6 +76,18 @@ static ssize_t ram_size_show(struct device *dev, struct device_attribute *attr,
 static struct device_attribute dev_attr_ram_size =
 	__ATTR(size, 0444, ram_size_show, NULL);
 
+static ssize_t ram_qtg_id_show(struct device *dev, struct device_attribute *attr,
+			       char *buf)
+{
+	struct cxl_memdev *cxlmd = to_cxl_memdev(dev);
+	struct cxl_dev_state *cxlds = cxlmd->cxlds;
+
+	return sysfs_emit(buf, "%d\n", cxlds->ram_qtg_id);
+}
+
+static struct device_attribute dev_attr_ram_qtg_id =
+	__ATTR(qtg_id, 0444, ram_qtg_id_show, NULL);
+
 static ssize_t pmem_size_show(struct device *dev, struct device_attribute *attr,
 			      char *buf)
 {
@@ -89,6 +101,18 @@ static ssize_t pmem_size_show(struct device *dev, struct device_attribute *attr,
 static struct device_attribute dev_attr_pmem_size =
 	__ATTR(size, 0444, pmem_size_show, NULL);
 
+static ssize_t pmem_qtg_id_show(struct device *dev, struct device_attribute *attr,
+				char *buf)
+{
+	struct cxl_memdev *cxlmd = to_cxl_memdev(dev);
+	struct cxl_dev_state *cxlds = cxlmd->cxlds;
+
+	return sysfs_emit(buf, "%d\n", cxlds->pmem_qtg_id);
+}
+
+static struct device_attribute dev_attr_pmem_qtg_id =
+	__ATTR(qtg_id, 0444, pmem_qtg_id_show, NULL);
+
 static ssize_t serial_show(struct device *dev, struct device_attribute *attr,
 			   char *buf)
 {
@@ -117,11 +141,13 @@ static struct attribute *cxl_memdev_attributes[] = {
 
 static struct attribute *cxl_memdev_pmem_attributes[] = {
 	&dev_attr_pmem_size.attr,
+	&dev_attr_pmem_qtg_id.attr,
 	NULL,
 };
 
 static struct attribute *cxl_memdev_ram_attributes[] = {
 	&dev_attr_ram_size.attr,
+	&dev_attr_ram_qtg_id.attr,
 	NULL,
 };
 





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