mb/google/rex: Add WWAN poweron sequencing

The PCIe WWAN module used on rex requires control over 4 signals to
successfully power it on. It is desirable to do this before passing
control to the payload, because the modem requires a ~10 seconds
initialization phase before it can be used.

The corrected sequence looks like:
1) Drive device into full reset and enable power in bootblock
2) Deassert FCPO in romstage, after power rails stabilize
3) Deassert WWAN_RST#, then WWAN_PERST# in ramstage

BUG=b:244077118
TEST=FM350 could be enumerated via lspci
Measured signals to check start-up Timing Sequence, tpr/ton1/ton2.
Tpr = 572mS
Ton1 = 6.3s
Ton2 = 6.3+4.17ms

Signed-off-by: Ivy Jian <ivy.jian@quanta.corp-partner.google.com>
Change-Id: I6cda9348ef7f54efe5ba2358040596a1c2da1b13
Reviewed-on: https://review.coreboot.org/c/coreboot/+/67332
Reviewed-by: Eric Lai <eric_lai@quanta.corp-partner.google.com>
Reviewed-by: Subrata Banik <subratabanik@google.com>
Reviewed-by: Tarun Tuli <taruntuli@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

0 files changed, 0 insertions, 0 deletions