[PATCH 1/2] PM: hibernate: add pm_hibernation_storing_image() helper

[Haowen Tu]

During hibernation, after create_image() saves the memory snapshot,
the kernel resumes devices with PMSG_THAW solely to write the hibernation
image to storage, then powers off.  Drivers for hardware not involved in
storage I/O have no reason to reinitialize during this transient phase.

Some subsystems, such as USB, do not expose the hibernation PM message
to driver resume callbacks, so drivers there need an explicit query to
distinguish the image-write phase from the final restore path.  Export
pm_hibernation_storing_image() for this purpose.

The implementation returns !!in_suspend, which is set to 1 in
create_image() just before swsusp_arch_suspend() and reset to 0 in
hibernate() after swsusp_write() completes.  Because in_suspend is
marked __nosavedata, it is not saved into the hibernation image; on the
restore path the variable remains 0 throughout, so the helper correctly
returns false during PMSG_RESTORE device resume.

Signed-off-by: Haowen Tu <tuhaowen@xxxxxxxxxxxxx>
---
 include/linux/suspend.h  |  2 ++
 kernel/power/hibernate.c | 19 +++++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/include/linux/suspend.h b/include/linux/suspend.h
index b02876f1ae38..28b454def83d 100644
--- a/include/linux/suspend.h
+++ b/include/linux/suspend.h
@@ -393,6 +393,7 @@ extern void hibernation_set_ops(const struct platform_hibernation_ops *ops);
 extern int hibernate(void);
 extern bool system_entering_hibernation(void);
 extern bool hibernation_available(void);
+extern bool pm_hibernation_storing_image(void);
 asmlinkage int swsusp_save(void);
 extern struct pbe *restore_pblist;
 int pfn_is_nosave(unsigned long pfn);
@@ -412,6 +413,7 @@ static inline void hibernation_set_ops(const struct platform_hibernation_ops *op
 static inline int hibernate(void) { return -ENOSYS; }
 static inline bool system_entering_hibernation(void) { return false; }
 static inline bool hibernation_available(void) { return false; }
+static inline bool pm_hibernation_storing_image(void) { return false; }
 
 static inline int hibernate_quiet_exec(int (*func)(void *data), void *data) {
 	return -ENOTSUPP;
diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
index af8d07bafe02..bc632cce40ff 100644
--- a/kernel/power/hibernate.c
+++ b/kernel/power/hibernate.c
@@ -113,6 +113,25 @@ bool hibernation_available(void)
 		!secretmem_active() && !cxl_mem_active();
 }
 
+/**
+ * pm_hibernation_storing_image - check if system is writing the hibernation image
+ *
+ * After create_image() saves a memory snapshot, the kernel briefly resumes
+ * devices with PMSG_THAW to write the image to storage before final powerdown.
+ * Drivers for hardware not involved in storage I/O may call this helper from
+ * their resume callbacks to skip unnecessary hardware initialization during
+ * that transient phase.
+ *
+ * Context: May be called from device PM callbacks.
+ * Return: %true if a hibernation snapshot has been taken and the system is
+ *         in the process of writing the image to persistent storage.
+ */
+bool pm_hibernation_storing_image(void)
+{
+	return !!in_suspend;
+}
+EXPORT_SYMBOL_GPL(pm_hibernation_storing_image);
+
 /**
  * hibernation_set_ops - Set the global hibernate operations.
  * @ops: Hibernation operations to use in subsequent hibernation transitions.
-- 
2.20.1