Re: [RFC PATCH 1/3] PM: hibernate: Nominally skip thaw sequence for all devices

[Mario Limonciello <superm1@kernel.org>]

On 10/13/25 12:58 PM, Rafael J. Wysocki wrote:
> On Mon, Oct 13, 2025 at 7:48 PM Mario Limonciello (AMD)
> <superm1@kernel.org> wrote:
>>
>> From: Mario Limonciello <mario.limonciello@amd.com>
>>
>> After the hibernation snapshot is created all devices will have
>> their thaw() callback called before the next stage.  For the most
>> common scenarios of hibernation this is not necessary because the
>> device will be powered off anyway.
> 
> And how exactly is the image going to be saved?
> 
> It is only in memory when the "thaw" callbacks are invoked.

Ah; right.

I suppose one option would be to thaw "just" the backing device, but 
this could turn into a relatively complex mess because it would have 
relationships (parent/child or device link) to other devices that need 
to thaw too then.

> 
>> If the hibernation snapshot was successfully created skip thawing
>> devices until it's needed for userspace created hibernation image
>> or hybrid sleep. To accomplish this use PMSG_INVALID in
>> hibernation_snapshot() and set the dpm functions to skip running.
>>
>> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
>> ---
>>   drivers/base/power/main.c |  6 ++++++
>>   kernel/power/hibernate.c  | 13 ++++++++++---
>>   kernel/power/user.c       |  3 +++
>>   3 files changed, 19 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
>> index 8179fd53171dc..58f5270a173e8 100644
>> --- a/drivers/base/power/main.c
>> +++ b/drivers/base/power/main.c
>> @@ -1143,6 +1143,9 @@ void dpm_resume(pm_message_t state)
>>          struct device *dev;
>>          ktime_t starttime = ktime_get();
>>
>> +       if (state.event == PM_EVENT_INVALID)
>> +               return;
>> +
>>          trace_suspend_resume(TPS("dpm_resume"), state.event, true);
>>
>>          pm_transition = state;
>> @@ -1245,6 +1248,9 @@ void dpm_complete(pm_message_t state)
>>   {
>>          struct list_head list;
>>
>> +       if (state.event == PM_EVENT_INVALID)
>> +               return;
>> +
>>          trace_suspend_resume(TPS("dpm_complete"), state.event, true);
>>
>>          INIT_LIST_HEAD(&list);
>> diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
>> index aadf82f57e868..7af2e392c574a 100644
>> --- a/kernel/power/hibernate.c
>> +++ b/kernel/power/hibernate.c
>> @@ -480,13 +480,14 @@ int hibernation_snapshot(int platform_mode)
>>          if (error || !in_suspend)
>>                  swsusp_free();
>>
>> -       msg = in_suspend ? (error ? PMSG_RECOVER : PMSG_THAW) : PMSG_RESTORE;
>> +       msg = in_suspend ? (error ? PMSG_RECOVER : PMSG_INVALID) : PMSG_RESTORE;
>>          dpm_resume(msg);
>>
>> -       if (error || !in_suspend)
>> +       if (error || !in_suspend) {
>>                  pm_restore_gfp_mask();
>> +               console_resume_all();
>> +       }
>>
>> -       console_resume_all();
>>          dpm_complete(msg);
>>
>>    Close:
>> @@ -707,7 +708,13 @@ static void power_down(void)
>>
>>   #ifdef CONFIG_SUSPEND
>>          if (hibernation_mode == HIBERNATION_SUSPEND) {
>> +               /* recover from hibernation_snapshot() */
>> +               dpm_resume(PMSG_THAW);
>> +               console_resume_all();
>> +               dpm_complete(PMSG_THAW);
>>                  pm_restore_gfp_mask();
>> +
>> +               /* run suspend sequence */
>>                  error = suspend_devices_and_enter(mem_sleep_current);
>>                  if (!error)
>>                          goto exit;
>> diff --git a/kernel/power/user.c b/kernel/power/user.c
>> index 3f9e3efb9f6e7..d70c963b1ba88 100644
>> --- a/kernel/power/user.c
>> +++ b/kernel/power/user.c
>> @@ -310,6 +310,9 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd,
>>                  pm_restore_gfp_mask();
>>                  error = hibernation_snapshot(data->platform_support);
>>                  if (!error) {
>> +                       dpm_resume(PMSG_THAW);
>> +                       console_resume_all();
>> +                       dpm_complete(PMSG_THAW);
>>                          error = put_user(in_suspend, (int __user *)arg);
>>                          data->ready = !freezer_test_done && !error;
>>                          freezer_test_done = false;
>> --
>> 2.43.0
>>