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