Re: [PATCH 1/2] PM: Allow device drivers to manage the frozen state of a device

[Muhammad Usama Anjum <usama.anjum@collabora.com>]

On 10/22/25 8:50 PM, Mario Limonciello wrote:
> From: "Mario Limonciello (AMD)" <superm1@kernel.org>
> 
> During a normal successful hibernate sequence devices will go through
> the freeze() callbacks create an image, go through the thaw() callbacks,
> and poweroff() callbacks.
> 
> During a successful hibernate sequence some device drivers may want to
> skip the thaw() callbacks.  This confuses the PM core though because it
> thinks the device is no longer suspended.
> 
> To accommodate drivers that want to do this, introduce a new is_frozen
> bit that the driver can set and manage.  From the driver perspective
> any thaw() or restore() callbacks that are being skipped should set
> is_frozen and return an error code.  The PM core will then put the
> device back into the list of devices to resume for any aborted hibernate.
> 
> Cc: Muhammad Usama Anjum <usama.anjum@collabora.com>
> Signed-off-by: Mario Limonciello (AMD) <superm1@kernel.org>
Tested-by: Muhammad Usama Anjum <usama.anjum@collabora.com>

> ---
>  Documentation/driver-api/pm/devices.rst | 8 ++++++++
>  drivers/base/power/main.c               | 5 +++++
>  include/linux/pm.h                      | 3 +++
>  3 files changed, 16 insertions(+)
> 
> diff --git a/Documentation/driver-api/pm/devices.rst b/Documentation/driver-api/pm/devices.rst
> index 36d5c9c9fd11..55c633727108 100644
> --- a/Documentation/driver-api/pm/devices.rst
> +++ b/Documentation/driver-api/pm/devices.rst
> @@ -578,6 +578,14 @@ should already have been stored during the ``freeze``, ``freeze_late`` or
>  the entire system, so it is not necessary for the callback to put the device in
>  a low-power state.
>  
> +Skipping thaw phase
> +-------------------
> +In some rare situations, it may be desirable to skip the thaw phases
> +(``thaw_noirq``, ``thaw_early``, ``thaw``) of a device entirely.  This can be
> +achieved by a device driver returning an error code from any of it's thaw
> +callbacks but also setting dev->power.is_frozen to true.  This indicates to the
> +PM core that the device is still in the frozen state.  The PM core will consider
> +this when resuming the device in later phases such as `restore` or `poweroff`.
>  
>  Leaving Hibernation
>  -------------------
> diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
> index e83503bdc1fd..451d54486645 100644
> --- a/drivers/base/power/main.c
> +++ b/drivers/base/power/main.c
> @@ -1100,6 +1100,11 @@ static void device_resume(struct device *dev, pm_message_t state, bool async)
>  
>   End:
>  	error = dpm_run_callback(callback, dev, state, info);
> +	/* device manages frozen state */
> +	if (error && dev->power.is_frozen) {
> +		dev->power.is_suspended = true;
> +		error = 0;
> +	}
>  
>  	device_unlock(dev);
>  	dpm_watchdog_clear(&wd);
> diff --git a/include/linux/pm.h b/include/linux/pm.h
> index cc7b2dc28574..52ee38d72aa2 100644
> --- a/include/linux/pm.h
> +++ b/include/linux/pm.h
> @@ -688,6 +688,9 @@ struct dev_pm_info {
>  #else
>  	bool			should_wakeup:1;
>  #endif
> +#ifdef CONFIG_HIBERNATE_CALLBACKS
> +	bool			is_frozen:1;	/* Owned by the driver */
> +#endif
>  #ifdef CONFIG_PM
>  	struct hrtimer		suspend_timer;
>  	u64			timer_expires;


-- 
---
Thanks,
Usama