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[RFC 1/2] PM / suspend: Add platform_suspend_target_state()

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  [RFC 1/2] PM / suspend: Add platform_suspend_target_state() Florian Fainelli <f.fainelli@gmail.com> - 2017-06-23 03:10 +0200
    Re: [RFC 1/2] PM / suspend: Add platform_suspend_target_state() "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-06-30 01:10 +0200

#1673156 — [RFC 1/2] PM / suspend: Add platform_suspend_target_state()

Add an optional platform_suspend_ops callback: target_state, and a
helper function globally visible to get this called:
platform_suspend_target_state().

This is useful for platform specific drivers that may need to take a
slightly different suspend/resume path based on the system's
suspend/resume state being entered.

Although this callback is optional and documented as such, it requires
a platform_suspend_ops::begin callback to be implemented in order to
provide an accurate suspend/resume state within the driver that
implements this platform_suspend_ops.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
---
 include/linux/suspend.h | 12 ++++++++++++
 kernel/power/suspend.c  | 15 +++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/include/linux/suspend.h b/include/linux/suspend.h
index d9718378a8be..d998a04a90a2 100644
--- a/include/linux/suspend.h
+++ b/include/linux/suspend.h
@@ -172,6 +172,15 @@ static inline void dpm_save_failed_step(enum suspend_stat_step step)
  *	Called by the PM core if the suspending of devices fails.
  *	This callback is optional and should only be implemented by platforms
  *	which require special recovery actions in that situation.
+ *
+ * @target_state: Returns the suspend state the suspend_ops will be entering.
+ * 	Called by device drivers that need to know the platform specific suspend
+ * 	state the system is about to enter.
+ * 	This callback is optional and should only be implemented by platforms
+ * 	which require special handling of power management states within
+ * 	drivers. It does require @begin to be implemented to provide the suspend
+ * 	state. Return value is platform_suspend_ops specific, and may be a 1:1
+ * 	mapping to suspend_state_t when relevant.
  */
 struct platform_suspend_ops {
 	int (*valid)(suspend_state_t state);
@@ -184,6 +193,7 @@ struct platform_suspend_ops {
 	bool (*suspend_again)(void);
 	void (*end)(void);
 	void (*recover)(void);
+	int (*target_state)(void);
 };
 
 struct platform_freeze_ops {
@@ -200,6 +210,7 @@ struct platform_freeze_ops {
  */
 extern void suspend_set_ops(const struct platform_suspend_ops *ops);
 extern int suspend_valid_only_mem(suspend_state_t state);
+extern int platform_suspend_target_state(void);
 
 extern unsigned int pm_suspend_global_flags;
 
@@ -279,6 +290,7 @@ static inline bool pm_resume_via_firmware(void) { return false; }
 
 static inline void suspend_set_ops(const struct platform_suspend_ops *ops) {}
 static inline int pm_suspend(suspend_state_t state) { return -ENOSYS; }
+static inline int platform_suspend_target_state(void) { return -ENOSYS; }
 static inline bool idle_should_freeze(void) { return false; }
 static inline void __init pm_states_init(void) {}
 static inline void freeze_set_ops(const struct platform_freeze_ops *ops) {}
diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c
index 15e6baef5c73..d31fe7a08f4a 100644
--- a/kernel/power/suspend.c
+++ b/kernel/power/suspend.c
@@ -177,6 +177,21 @@ void suspend_set_ops(const struct platform_suspend_ops *ops)
 EXPORT_SYMBOL_GPL(suspend_set_ops);
 
 /**
+ * platform_suspend_target_state - Return the platform specific suspend state.
+ * a begin() callback is necessary in order to fill this information correctly
+ * for callers.
+ */
+int platform_suspend_target_state(void)
+{
+	if (!suspend_ops || !suspend_ops->target_state ||
+	    (suspend_ops->target_state && !suspend_ops->begin))
+		return -ENOTSUPP;
+
+	return suspend_ops->target_state();
+}
+EXPORT_SYMBOL_GPL(platform_suspend_target_state);
+
+/**
  * suspend_valid_only_mem - Generic memory-only valid callback.
  *
  * Platform drivers that implement mem suspend only and only need to check for
-- 
2.9.3

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#1678273

On Thursday, June 22, 2017 06:08:36 PM Florian Fainelli wrote:
> Add an optional platform_suspend_ops callback: target_state, and a
> helper function globally visible to get this called:
> platform_suspend_target_state().
> 
> This is useful for platform specific drivers that may need to take a
> slightly different suspend/resume path based on the system's
> suspend/resume state being entered.
> 
> Although this callback is optional and documented as such, it requires
> a platform_suspend_ops::begin callback to be implemented in order to
> provide an accurate suspend/resume state within the driver that
> implements this platform_suspend_ops.
> 
> Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
> ---
>  include/linux/suspend.h | 12 ++++++++++++
>  kernel/power/suspend.c  | 15 +++++++++++++++
>  2 files changed, 27 insertions(+)
> 
> diff --git a/include/linux/suspend.h b/include/linux/suspend.h
> index d9718378a8be..d998a04a90a2 100644
> --- a/include/linux/suspend.h
> +++ b/include/linux/suspend.h
> @@ -172,6 +172,15 @@ static inline void dpm_save_failed_step(enum suspend_stat_step step)
>   *	Called by the PM core if the suspending of devices fails.
>   *	This callback is optional and should only be implemented by platforms
>   *	which require special recovery actions in that situation.
> + *
> + * @target_state: Returns the suspend state the suspend_ops will be entering.
> + * 	Called by device drivers that need to know the platform specific suspend
> + * 	state the system is about to enter.
> + * 	This callback is optional and should only be implemented by platforms
> + * 	which require special handling of power management states within
> + * 	drivers. It does require @begin to be implemented to provide the suspend
> + * 	state. Return value is platform_suspend_ops specific, and may be a 1:1
> + * 	mapping to suspend_state_t when relevant.
>   */
>  struct platform_suspend_ops {
>  	int (*valid)(suspend_state_t state);
> @@ -184,6 +193,7 @@ struct platform_suspend_ops {
>  	bool (*suspend_again)(void);
>  	void (*end)(void);
>  	void (*recover)(void);
> +	int (*target_state)(void);

I would use unsigned int (the sign should not matter).

>  };

That's almost what I was thinking about except that the values returned by
->target_state should be unique, so it would be good to do something to
ensure that.

The concern is as follows.

Say you have a driver develped for platform X where ->target_state returns
A for "mem" and B for "standby".  Then, the same IP is re-used on platform Y
returning B for "mem" and C for "standby" and now the driver cannot
distinguish between them.

Moreover, even if they both returned A for "mem" there might be differences
in how "mem" was defined by each of them and therefore in what the driver was
expected to do to handle "mem" on X and Y.

Thanks,
Rafael

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