[PATCH v4] kernel.h: add comments for system_states

Randy Dunlap
2025-09-04T06:36:34Z

Provide some basic comments about the system_states and what they imply.
Also convert the comments to kernel-doc format.

However, kernel-doc does not support kernel-doc notation on extern
struct/union/typedef/enum/etc. So I made this a DOC: block so that
I can use (insert) it into a Documentation (.rst) file and have it
look decent.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Rafael J. Wysocki <rafael@kernel.org> # v1
---
v2: add Rafael's Ack.
v3: add Andrew
v4: add DOC: so that this DOC: block can be used in Documentation/
add Greg K-H
add Jon Corbet, Mauro Chehab, & linux-doc

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Len Brown <len.brown@intel.com>
Cc: linux-pm@vger.kernel.org
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
---
Documentation/driver-api/pm/devices.rst | 8 ++++++++
include/linux/kernel.h | 18 ++++++++++++++++--
2 files changed, 24 insertions(+), 2 deletions(-)

--- linux-next-20250819.orig/include/linux/kernel.h
+++ linux-next-20250819/include/linux/kernel.h
@@ -164,8 +164,22 @@ extern int root_mountflags;

extern bool early_boot_irqs_disabled;

-/*
- * Values used for system_state. Ordering of the states must not be changed
+/**
+ * DOC: General system_states available for drivers
+ *
+ * enum system_states - Values used for system_state.
+ *
+ * * @SYSTEM_BOOTING: %0, no init needed
+ * * @SYSTEM_SCHEDULING: system is ready for scheduling; OK to use RCU
+ * * @SYSTEM_FREEING_INITMEM: system is freeing all of initmem; almost running
+ * * @SYSTEM_RUNNING: system is up and running
+ * * @SYSTEM_HALT: system entered clean system halt state
+ * * @SYSTEM_POWER_OFF: system entered shutdown/clean power off state
+ * * @SYSTEM_RESTART: system entered emergency power off or normal restart
+ * * @SYSTEM_SUSPEND: system entered suspend or hibernate state
+ *
+ * Note:
+ * Ordering of the states must not be changed
* as code checks for <, <=, >, >= STATE.
*/
extern enum system_states {
--- linux-next-20250819.orig/Documentation/driver-api/pm/devices.rst
+++ linux-next-20250819/Documentation/driver-api/pm/devices.rst
@@ -241,6 +241,14 @@ before reactivating its class I/O queues
More power-aware drivers might prepare the devices for triggering system wakeup
events.

+System states available for drivers
+-----------------------------------
+
+These system states are available for drivers to help them determine how to
+handle state transitions.
+
+.. kernel-doc:: include/linux/kernel.h
+ :doc: General system_states available for drivers

Call Sequence Guarantees
------------------------