soc/intel/cmn/gfx: Add API to report presence of external display

This patch implements an API to report the presence of an external
display on Intel silicon. The API uses information from the transcoder
and framebuffer to determine if an external display is connected.

For example, if the transcoder is attached to any DDI ports other than
DDI-A (eDP), and the framebuffer is initialized, then it is likely
that an external display is present.

This information can be used by payloads to determine whether or not
to power on the display, even if eDP is not initialized.

BUG=b:299137940
TEST=Build and boot google/rex

Scenarios:

Booting with eDP alone: has_external_display value is 0
Booting with eDP + HDMI: has_external_display value is 0
Booting with HDMI alone: has_external_display value is 1
Booting with USB-C display alone: has_external_display value is 1

Change-Id: I77436940978c7fa9368d79394b46a5e794c32e42
Signed-off-by: Subrata Banik <subratabanik@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/78080
Reviewed-by: Julius Werner <jwerner@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nick Vaccaro <nvaccaro@google.com>
Reviewed-by: Eric Lai <ericllai@google.com>

0 files changed, 0 insertions, 0 deletions