power/intel_x86: Fix S0ix suspend/resume hook notifications
power/intel_x86: Fix S0ix suspend/resume hook notifications

There is a fundamental difference in host behavior w.r.t. S3 and
S0ix. When the host enters S3, it asserts the SLP_S3# signal until it
is woken back up. Thus, EC depends on the SLP_S3# signal state to
decide when to notify listeners about CHIPSET_SUSPEND and
CHIPSET_RESUME state.

With S0ix, SLP_S0# signal is asserted whenever host enters
S0ix. However, periodically (every 8 seconds), the host wakes up for
some bookkeeping activities, but does not come out of the low power
mode completely. This bookkeeping activity takes ~2-5 ms and the host
goes back into S0ix state. Because of this periodic activity, SLP_S0#
signal is de-asserted and asserted back every 8 seconds.

Thus, if the power state machine depends solely on the SLP_S0# signal
to notify CHIPSET_SUSPEND and CHIPSET_RESUME states, then all the
listeners would be performing unnecessary actions every 8
seconds. This leads to a number of side-effects including:
1. Dual-role toggle being enabled and disabled every 8 seconds.
2. Power spikes in EC power consumption during S0ix every 8 seconds.

In order to avoid the side-effects of periodic host activity in S0ix,
this change adds a new flag s0ix_notify, which is set based on the
notifications that are pending based on host sleep event.

On receiving host sleep event for S0ix suspend, s0ix_notify will be
set to S0IX_NOTIFY_SUSPEND. Next, whenever SLP_S0# is asserted,
power_state machine notifies listeners of CHIPSET_SUSPEND
and resets s0ix_notify flag to S0IX_NOTIFY_NONE. Thus, all future
assertions of SLP_S0# do not result in the suspend notification.

Similarly, on resume, power_state machine will not notify
CHIPSET_RESUME on SLP_S0# deassertion. Instead the host sleep event
for S0ix resume will set s0ix_notify flag to S0IX_NOTIFY_RESUME and
wake chipset task. The power state machine in turn will notify
listeners of the resume event and reset s0ix_notify flag.

BUG=b:65356050,b:67750352
BRANCH=None
TEST=Verified that the CHIPSET_SUSPEND/CHIPSET_RESUME notification
happens only once during a system suspend/resume cycle. Periodic host
wakes for book-keeping activities do not result in
CHIPSET_SUSPEND/CHIPSET_RESUME notifications.

Change-Id: Idf253b9393a0c25ff2eac63c60ddbcd3af954818
Signed-off-by: Furquan Shaikh <6be5c96c464778f89679b1062a2e0a6af93d2aa5@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/729478
Reviewed-by: Aaron Durbin <af0622ab041e8b0f8e5819838dcc93898196e71f@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec