A CXL region whose capacity is online as System RAM must be taken
offline before a Secondary Bus Reset of the CXL Downstream Port it is
reached through.

Add cxl_offline_memory() to offline the memory blocks spanning a
physical range, exported in the CXL_MHP namespace since the CXL core is
its only caller.

Signed-off-by: Fabio M. De Francesco <fabio.m.de.francesco@linux.intel.com>
---
 drivers/base/memory.c  | 36 ++++++++++++++++++++++++++++++++++++
 include/linux/memory.h |  5 +++++
 2 files changed, 41 insertions(+)

diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index bcfe2d9f4adb..ce89b251d34a 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -1018,6 +1018,42 @@ int walk_memory_blocks(unsigned long start, unsigned long size,
 	return ret;
 }
 
+static int cxl_offline_memory_block(struct memory_block *mem, void *arg)
+{
+	int rc = device_offline(&mem->dev);
+
+	/* device_offline() returns a positive value when already offline. */
+	if (rc > 0)
+		return 0;
+
+	return rc;
+}
+
+/**
+ * cxl_offline_memory - offline the memory blocks spanning a physical range
+ * @start: start of the range, memory-block aligned
+ * @size: size of the range, a multiple of the memory block size
+ *
+ * Offline every memory block in [start, start + size). The blocks are offlined
+ * but not removed, so the range can be brought back online afterward. The
+ * caller owns the range and this performs no validation on it.
+ *
+ * Return: 0 on success, negative errno if a block cannot be offlined.
+ *
+ * Context: process context. Sleeps and takes the memory hotplug lock.
+ */
+int cxl_offline_memory(u64 start, u64 size)
+{
+	int rc;
+
+	lock_device_hotplug();
+	rc = walk_memory_blocks(start, size, NULL, cxl_offline_memory_block);
+	unlock_device_hotplug();
+
+	return rc;
+}
+EXPORT_SYMBOL_NS_GPL(cxl_offline_memory, "CXL_MHP");
+
 struct for_each_memory_block_cb_data {
 	walk_memory_blocks_func_t func;
 	void *arg;
diff --git a/include/linux/memory.h b/include/linux/memory.h
index 463dc02f6cff..5dc0b96fb004 100644
--- a/include/linux/memory.h
+++ b/include/linux/memory.h
@@ -149,6 +149,10 @@ static inline unsigned long memory_block_advised_max_size(void)
 {
 	return 0;
 }
+static inline int cxl_offline_memory(u64 start, u64 size)
+{
+	return 0;
+}
 #else /* CONFIG_MEMORY_HOTPLUG */
 extern int register_memory_notifier(struct notifier_block *nb);
 extern void unregister_memory_notifier(struct notifier_block *nb);
@@ -167,6 +171,7 @@ typedef int (*walk_memory_blocks_func_t)(struct memory_block *, void *);
 extern int walk_memory_blocks(unsigned long start, unsigned long size,
 			      void *arg, walk_memory_blocks_func_t func);
 extern int for_each_memory_block(void *arg, walk_memory_blocks_func_t func);
+int cxl_offline_memory(u64 start, u64 size);
 
 extern int memory_group_register_static(int nid, unsigned long max_pages);
 extern int memory_group_register_dynamic(int nid, unsigned long unit_pages);
-- 
2.55.0