lynxpoint/broadwell: fix PCH power optimizer

Setting both bits 27 and 7 of PCH register PMSYNC_CFG (PMSYNC
Configuration; offset 0x33c8) causes pre-OS display init to fail
on HSW-U/Lynxpoint and BDW-U ChromeOS devices when the VBIOS/GOP
driver is run after the register is set. A re-examination of
Intel's reference code reveals that bit 7 should be set for the
LP PCH, and bit 27 for non-LP, but not both simultaneously.

The previous workaround was to disable the entire power optimizer
section via a Kconfig option, which isn't ideal.

Test: unset bit 27 of PMSYNC_CFG and boot google/lulu,
observe functional pre-OS video output

Change-Id: I446e169d23dd446710a1648f0a9b9599568b80aa
Signed-off-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-on: https://review.coreboot.org/18385
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>
Reviewed-by: Duncan Laurie <dlaurie@chromium.org>

0 files changed, 0 insertions, 0 deletions