[PATCH 0/2] PM: hibernate: add helper to detect image-write phase

[Haowen Tu]

During S4 hibernation, after create_image() saves the memory snapshot,
the kernel resumes devices with PMSG_THAW solely to write the hibernation
image to storage before final powerdown.  Drivers unrelated to storage I/O
have no reason to reinitialize during this transient phase.

Drivers using dev_pm_ops already have separate .thaw and .restore
callbacks and can handle this natively.  However, usb_driver.resume
takes no pm_message_t argument, so a USB driver cannot distinguish
PMSG_THAW from PMSG_RESTORE without an out-of-band query.

This series adds pm_hibernation_storing_image(), a small helper that
returns true during the image-write window.  As a first user, the UVC
driver uses it to skip resume in uvc_video_resume() until the real
PMSG_RESTORE wake-up.

Tested with hibernation image written to local storage and resumed from
disk on a system with a USB UVC camera attached.

Haowen Tu (2):
  pm/hibernate: add pm_hibernation_storing_image() helper
  media: uvcvideo: skip resume when writing hibernation image

 drivers/media/usb/uvc/uvc_video.c | 10 ++++++++++
 include/linux/suspend.h           |  2 ++
 kernel/power/hibernate.c          | 19 +++++++++++++++++++
 3 files changed, 31 insertions(+)

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2.20.1