[PATCH v11 05/31] cxl/mem: Expose dynamic ram 1 partition in sysfs

[Anisa Su]

From: Ira Weiny <iweiny@xxxxxxxxxx>

To properly configure CXL regions user space will need to know the
details of the dynamic ram partition.

Expose the first dynamic ram partition through sysfs.

Signed-off-by: Ira Weiny <iweiny@xxxxxxxxxx>
Signed-off-by: Anisa Su <anisa.su@xxxxxxxxxxx>
Reviewed-by: Dave Jiang <dave.jiang@xxxxxxxxx>

---
Changes:
1. Documentation: bump kernel version to 7.3 and date to June 2026
2. Pick up Dave's reviewed-by tag
3. Rename dynamic_ram_a to dynamic_ram_1
---
 Documentation/ABI/testing/sysfs-bus-cxl | 24 +++++++++++
 drivers/cxl/core/memdev.c               | 57 +++++++++++++++++++++++++
 2 files changed, 81 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-bus-cxl b/Documentation/ABI/testing/sysfs-bus-cxl
index 16a9b3d2e2c0..435495de409c 100644
--- a/Documentation/ABI/testing/sysfs-bus-cxl
+++ b/Documentation/ABI/testing/sysfs-bus-cxl
@@ -89,6 +89,30 @@ Description:
 		and there are platform specific performance related
 		side-effects that may result. First class-id is displayed.
 
+What:		/sys/bus/cxl/devices/memX/dynamic_ram_1/size
+Date:		June, 2026
+KernelVersion:	v7.3
+Contact:	linux-cxl@xxxxxxxxxxxxxxx
+Description:
+		(RO) The first Dynamic RAM partition capacity as bytes.
+
+
+What:		/sys/bus/cxl/devices/memX/dynamic_ram_1/qos_class
+Date:		June, 2026
+KernelVersion:	v7.3
+Contact:	linux-cxl@xxxxxxxxxxxxxxx
+Description:
+		(RO) For CXL host platforms that support "QoS Telemmetry"
+		this attribute conveys a comma delimited list of platform
+		specific cookies that identifies a QoS performance class
+		for the partition of the CXL mem device. These
+		class-ids can be compared against a similar "qos_class"
+		published for a root decoder. While it is not required
+		that the endpoints map their local memory-class to a
+		matching platform class, mismatches are not recommended
+		and there are platform specific performance related
+		side-effects that may result. First class-id is displayed.
+
 
 What:		/sys/bus/cxl/devices/memX/serial
 Date:		January, 2022
diff --git a/drivers/cxl/core/memdev.c b/drivers/cxl/core/memdev.c
index 71602820f896..20417db933aa 100644
--- a/drivers/cxl/core/memdev.c
+++ b/drivers/cxl/core/memdev.c
@@ -101,6 +101,19 @@ 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 dynamic_ram_1_size_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;
+	unsigned long long len = cxl_part_size(cxlds, CXL_PARTMODE_DYNAMIC_RAM_1);
+
+	return sysfs_emit(buf, "%#llx\n", len);
+}
+
+static struct device_attribute dev_attr_dynamic_ram_1_size =
+	__ATTR(size, 0444, dynamic_ram_1_size_show, NULL);
+
 static ssize_t serial_show(struct device *dev, struct device_attribute *attr,
 			   char *buf)
 {
@@ -443,6 +456,25 @@ static struct attribute *cxl_memdev_pmem_attributes[] = {
 	NULL,
 };
 
+static ssize_t dynamic_ram_1_qos_class_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",
+			  part_perf(cxlds, CXL_PARTMODE_DYNAMIC_RAM_1)->qos_class);
+}
+
+static struct device_attribute dev_attr_dynamic_ram_1_qos_class =
+	__ATTR(qos_class, 0444, dynamic_ram_1_qos_class_show, NULL);
+
+static struct attribute *cxl_memdev_dynamic_ram_1_attributes[] = {
+	&dev_attr_dynamic_ram_1_size.attr,
+	&dev_attr_dynamic_ram_1_qos_class.attr,
+	NULL,
+};
+
 static ssize_t ram_qos_class_show(struct device *dev,
 				  struct device_attribute *attr, char *buf)
 {
@@ -519,6 +551,29 @@ static struct attribute_group cxl_memdev_pmem_attribute_group = {
 	.is_visible = cxl_pmem_visible,
 };
 
+static umode_t cxl_dynamic_ram_1_visible(struct kobject *kobj, struct attribute *a, int n)
+{
+	struct device *dev = kobj_to_dev(kobj);
+	struct cxl_memdev *cxlmd = to_cxl_memdev(dev);
+	struct cxl_dpa_perf *perf = part_perf(cxlmd->cxlds, CXL_PARTMODE_DYNAMIC_RAM_1);
+
+	if (a == &dev_attr_dynamic_ram_1_qos_class.attr &&
+	    (!perf || perf->qos_class == CXL_QOS_CLASS_INVALID))
+		return 0;
+
+	if (a == &dev_attr_dynamic_ram_1_size.attr &&
+	    (!cxl_part_size(cxlmd->cxlds, CXL_PARTMODE_DYNAMIC_RAM_1)))
+		return 0;
+
+	return a->mode;
+}
+
+static struct attribute_group cxl_memdev_dynamic_ram_1_attribute_group = {
+	.name = "dynamic_ram_1",
+	.attrs = cxl_memdev_dynamic_ram_1_attributes,
+	.is_visible = cxl_dynamic_ram_1_visible,
+};
+
 static umode_t cxl_memdev_security_visible(struct kobject *kobj,
 					   struct attribute *a, int n)
 {
@@ -547,6 +602,7 @@ static const struct attribute_group *cxl_memdev_attribute_groups[] = {
 	&cxl_memdev_attribute_group,
 	&cxl_memdev_ram_attribute_group,
 	&cxl_memdev_pmem_attribute_group,
+	&cxl_memdev_dynamic_ram_1_attribute_group,
 	&cxl_memdev_security_attribute_group,
 	NULL,
 };
@@ -555,6 +611,7 @@ void cxl_memdev_update_perf(struct cxl_memdev *cxlmd)
 {
 	sysfs_update_group(&cxlmd->dev.kobj, &cxl_memdev_ram_attribute_group);
 	sysfs_update_group(&cxlmd->dev.kobj, &cxl_memdev_pmem_attribute_group);
+	sysfs_update_group(&cxlmd->dev.kobj, &cxl_memdev_dynamic_ram_1_attribute_group);
 }
 EXPORT_SYMBOL_NS_GPL(cxl_memdev_update_perf, "CXL");
 
-- 
2.43.0