cxl/region: Add a region sysfs interface for region lock status

There are 3 scenarios that leads to a locked region:
1. A region is created on a root decoder with Fixed Device Confiuration
   attribute.
2. CXL_HDM_DECODER0_CTRL_LOCK.

Both 1 & 1 are well described in:
commit 2230c4b ("cxl: Add handling of locked CXL decoder")

3) Platform that has region creation with PRMT address translation always
   locks the region, regardless of the FIXED attribute or decoder ctrl bit.

Region locked means region destroy operations are not permitted. CXL
region driver returns -EPERM for region destroy operations.

Although the locked status of the corresponding root decoder implies the
region is also locked, exposing the region lock status directly to
userspace improves usability for users who may not be aware of this
relationship.

[ dj: Amended commit log with additional locking scenarios. ]

Signed-off-by: Li Ming <ming.li@zohomail.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Alejandro Lucero <alucerop@amd.com>
Reviewed-by: Alison Schofield <alison.schofield@intel.com>
Link: https://patch.msgid.link/20260401124951.1290041-1-ming.li@zohomail.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>

Author: liming011

Documentation/ABI/testing/sysfs-bus-cxl

@@ -508,6 +508,19 @@ Description:
 		(RO) The size of extended linear cache, if there is an extended
 		linear cache. Otherwise the attribute will not be visible.
 
+
+What:		/sys/bus/cxl/devices/regionZ/locked
+Date:		Mar, 2026
+KernelVersion:	v7.1
+Contact:	linux-cxl@vger.kernel.org
+Description:
+		(RO) The CXL driver has the capability to lock a region based on
+		a BIOS or platform dependent configuration. Regions created as
+		locked are never permitted to be destroyed. Resets to participating
+		decoders will not result in a region destroy and will not free the
+		decoder resources.
+
+
 What:		/sys/bus/cxl/devices/regionZ/mode
 Date:		January, 2023
 KernelVersion:	v6.3

drivers/cxl/core/region.c

@@ -767,6 +767,22 @@ static ssize_t extended_linear_cache_size_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(extended_linear_cache_size);
 
+static ssize_t locked_show(struct device *dev,
+			   struct device_attribute *attr,
+			   char *buf)
+{
+	struct cxl_region *cxlr = to_cxl_region(dev);
+	int rc;
+
+	ACQUIRE(rwsem_read_intr, rwsem)(&cxl_rwsem.region);
+	if ((rc = ACQUIRE_ERR(rwsem_read_intr, &rwsem)))
+		return rc;
+
+	rc = test_bit(CXL_REGION_F_LOCK, &cxlr->flags);
+	return sysfs_emit(buf, "%d\n", rc);
+}
+static DEVICE_ATTR_RO(locked);
+
 static struct attribute *cxl_region_attrs[] = {
 	&dev_attr_uuid.attr,
 	&dev_attr_commit.attr,
@@ -776,6 +792,7 @@ static struct attribute *cxl_region_attrs[] = {
 	&dev_attr_size.attr,
 	&dev_attr_mode.attr,
 	&dev_attr_extended_linear_cache_size.attr,
+	&dev_attr_locked.attr,
 	NULL,
 };