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    SubjectRe: [RFC 1/2] PM / suspend: Add platform_suspend_target_state()
    On Sat 2017-07-15 00:16:16, Rafael J. Wysocki wrote:
    > On Wednesday, July 12, 2017 11:08:19 AM Florian Fainelli wrote:
    > > On 06/29/2017 04:00 PM, Rafael J. Wysocki wrote:
    > > > 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.
    > >
    > > 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.

    Remind me why this is good idea?

    We currently have 1364+ boards in tree. That will be rather large
    enum.

    If board wants to know if certain regulator stays online during
    suspend, it should invent an API for _that_.
    Pavel

    --
    (english) http://www.livejournal.com/~pavelmachek
    (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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