Re: [PATCH v2 1/2] PM / wakeup: Add callback for wake-up change notification

[Geert Uytterhoeven]

Hi Rafael,

On Tue, Jun 19, 2018 at 4:48 PM Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote:
> On Tue, Jun 19, 2018 at 3:55 PM, Geert Uytterhoeven
> <geert+renesas@xxxxxxxxx> wrote:
> > Add a callback to inform a device that its wake-up setting has been
> > changed.  This allows a device to synchronize device configuration with
> > an external user action.
> >
> > E.g. on systems using a Rohm BD9571MWV PMIC and a toggle accessory power
> > switch, the system suspend/resume procedure is:
> >   1. Configure PMIC for DDR backup mode (by software), which changes the
> >      role of the accessory power switch from a power to a wake-up
> >      switch,
> >   2. Switch accessory power switch off (manually), to prepare for system
> >      suspend,
> >   3. Suspend system (by software),
> >   4. Switch accessory power switch on (manually), to wake up the system.
> >
> > As step 2 involves a manual operation, step 1 cannot be combined
> > with step 3 and performed in the PMIC's suspend callback (unlike on
> > systems with a momentary power switch).
> >
> > Adding the new callback allows to move step 1 to the new callback, to be
> > performed in response to the user writing "enabled" to the PMIC's
> > "wakeup" virtual file in sysfs.
>
> I still don't quite understand this TBH.
>
> In particular, why do you want a write to "wakeup" trigger this
> instead of having a special sysfs attr for that exposed by your PMIC
> driver?

In v1 (https://patchwork.kernel.org/patch/9996567/), I had a
driver-specific "backup_mode" sysfs file.
In v2 and later of the driver series (https://lkml.org/lkml/2018/4/18/345),
I changed that to use the standard "wakeup" file in sysfs, in response to
a comment from Mark Brown.

> Writing "enabled" to "wakeup" for the PMIC should enable the PMIC
> itself to wake up the system, which isn't quite the case, or is it?

Actually the PMIC cannot wake up the system if backup mode is not enabled.
When suspending the system (PSCI suspend) without enabling backup mode
first, the system will just crash (which cannot be distinguished from being
suspended, as PSCI doesn't support any other wake-up sources anyway[*] ;-)
So in that sense writing "enabled" to the "wakeup" file does enable the
PMIC to wake up the system.

Do you still prefer a driver-specific sysfs file?
Thanks!

[*] Perhaps you remember my ill-received attempt to prevent the system from
    using PSCI system suspend when any other wake-up sources were enabled?
    ("[PATCH/RFC 0/6] PSCI: Fix non-PMIC wake-up if SYSTEM_SUSPEND cuts
     power", https://lkml.org/lkml/2017/2/20/566).

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds