On Wednesday, July 12, 2017 11:08:19 AM Florian Fainelli wrote:

On 06/29/2017 04:00 PM, Rafael J. Wysocki wrote:

quoted

On Thursday, June 22, 2017 06:08:36 PM Florian Fainelli wrote:

quoted

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).

quoted

 };

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.

That makes sense, would you need the core implementation in
platform_suspend_target_state() to range check what
suspend_ops->target_state() returns against a set of reserved value say,
checking from 0 up to ACPI_S_STATE_COUNT or is there another range you
would like to see being used?

I had an idea of using an enum type encompassing all of the power states
defined for various platforms and serving both as a registry (to ensure the
uniqueness of the values assigned to the states) and a common ground
between platforms and drivers.

Something like:

enum platform_target_state {
	PLATFORM_STATE_UNKNOWN = -1,
	PLATFORM_STATE_WORKING = 0,
	PLATFORM_STATE_ACPI_S1,
	PLATFORM_STATE_ACPI_S2,
	PLATFORM_STATE_ACPI_S3,
	PLATFORM_STATE_MY_BOARD_1_GATE_CLOCKS,
	PLATFORM_STATE_MY_BOARD_1_GATE_POWER,
	PLATFORM_STATE_ANOTHER_BOARD_DO_CRAZY_STUFF,
	...
};

and define ->target_state to return a value of this type.

Then, if a driver sees one of these and recognizes that value, it should
know exactly what to do.

Thanks,
Rafael