soc/intel/common/pmc: Avoid unnecessary writes of AFTERG3_EN

pmc_set_power_failure_state() is usually called twice, once upon boot
(with `target_on == true`) and once from SMM when the system is shut
down (with `target_on == false`). Assuming settings didn't change
between these calls, there is only one case where we actually need
to write the register value: when updating the state for the
MAINBOARD_POWER_STATE_PREVIOUS feature.

This suits us well as we want to avoid unnecessary writes so we
don't clobber the value set upon boot from within SMM. Due to
inaccessible option backends, SMM might not know the current
option state.

The assumption above, that the option value didn't change, may not
be true if the user changed the option on purpose. In the future,
one would have to reboot the machine for option changes to take
effect. However, this doesn't seem to make a huge difference: One
already needed a controlled shutdown for the update to take effect
before. A reboot doesn't seem much more expensive.

Change-Id: I58dd74b8b073f4f07db090bf7fddb14b5df8239a
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/55539
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

0 files changed, 0 insertions, 0 deletions