[PATCH v2 20/21] cxl: Export sysfs attributes for memory device QTG ID

From: Dave Jiang <dave.jiang@intel.com>
To: linux-cxl@vger.kernel.org, linux-acpi@vger.kernel.org
Cc: Dan Williams <dan.j.williams@intel.com>,
	dan.j.williams@intel.com, ira.weiny@intel.com,
	vishal.l.verma@intel.com, alison.schofield@intel.com,
	rafael@kernel.org, lukas@wunner.de
Subject: [PATCH v2 20/21] cxl: Export sysfs attributes for memory device QTG ID
Date: Mon, 27 Mar 2023 14:46:06 -0700	[thread overview]
Message-ID: <167995356611.2857312.4634198260468536572.stgit@djiang5-mobl3> (raw)
In-Reply-To: <167995336797.2857312.539473939839316778.stgit@djiang5-mobl3>

Export qtg_id sysfs attributes for the CXL memory device. The QTG ID
should show up as /sys/bus/cxl/devices/memX/qtg_id. The QTG ID is
retrieved via _DSM after supplying the caluclated 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 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@intel.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
---
 Documentation/ABI/testing/sysfs-bus-cxl |   11 +++++++++++
 drivers/cxl/core/memdev.c               |   15 +++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-bus-cxl b/Documentation/ABI/testing/sysfs-bus-cxl
index 471ac9a37078..a018f0a21aca 100644
--- a/Documentation/ABI/testing/sysfs-bus-cxl
+++ b/Documentation/ABI/testing/sysfs-bus-cxl
@@ -58,6 +58,17 @@ Description:
 		affinity for this device.
 
 
+What:		/sys/bus/cxl/devices/memX/qtg_id
+Date:		March, 2024
+KernelVersion:	v6.4
+Contact:	linux-cxl@vger.kernel.org
+Description:
+		(RO) Show the first QoS Throttling Group ID for the device.
+		The ID is used to match against the CFMWS (root decoder)
+		QTG ID so that the memory range under a hot-plugged device
+		is assigned under the appropriate CFMWS.
+
+
 What:		/sys/bus/cxl/devices/*/devtype
 Date:		June, 2021
 KernelVersion:	v5.14
diff --git a/drivers/cxl/core/memdev.c b/drivers/cxl/core/memdev.c
index d2605fc39240..974eff833edd 100644
--- a/drivers/cxl/core/memdev.c
+++ b/drivers/cxl/core/memdev.c
@@ -106,12 +106,27 @@ static ssize_t numa_node_show(struct device *dev, struct device_attribute *attr,
 }
 static DEVICE_ATTR_RO(numa_node);
 
+static ssize_t qtg_id_show(struct device *dev, struct device_attribute *attr,
+			   char *buf)
+{
+	struct cxl_memdev *cxlmd = to_cxl_memdev(dev);
+	struct qos_prop_entry *qos;
+
+	if (list_empty(&cxlmd->qos_list))
+		return 0;
+
+	qos = list_first_entry(&cxlmd->qos_list, struct qos_prop_entry, list);
+	return sysfs_emit(buf, "%u\n", qos->qtg_id);
+}
+static DEVICE_ATTR_RO(qtg_id);
+
 static struct attribute *cxl_memdev_attributes[] = {
 	&dev_attr_serial.attr,
 	&dev_attr_firmware_version.attr,
 	&dev_attr_payload_max.attr,
 	&dev_attr_label_storage_size.attr,
 	&dev_attr_numa_node.attr,
+	&dev_attr_qtg_id.attr,
 	NULL,
 };
 


