soc/intel/alderlake: Pick an unused and safer graphics address space

It turns out that the [0xfa000000-0xfaffffff] range conflicts with
some North TraceHub address space ranges ([0xfad00000-0xfadfffff] and
[0xfacfc000-0xfacfffff]).

Experiments have established that this conflicting range results in an
unpected PIPE A underrun issue reported by i915 and some visible
flickers on the display during boot.

The [0xf0000000-0xffffffff] range is a crowded memory space with
resources statically assigned to some devices but also some ranges
used at various point in the boot flow by the FSP.

To not run into any other potential conflicts, we want to pick a
unused memory space. But at this early stage of the boot, we do not
have full knowledge of what memory space is going to be used by the
FSP. As a result, we decided to pick the [0xaf000000-0xafffffff] range
as:

1. It does not conflicting with any coreboot memory space usage
2. It is the address the FSP uses by default for GFX MMIO BAR0 and as
   such should not conflict with any FSP memory space usage.

BUG=b:264648959
BRANCH=firmware-brya-14505.B
TEST=No flickers observed on boot

Change-Id: I6a00350ff4007bb7692d2ff6598b946cc6123302
Signed-off-by: Jeremy Compostella <jeremy.compostella@intel.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/72605
Reviewed-by: YH Lin <yueherngl@google.com>
Reviewed-by: Tarun Tuli <taruntuli@google.com>
Reviewed-by: Subrata Banik <subratabanik@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Kapil Porwal <kapilporwal@google.com>

0 files changed, 0 insertions, 0 deletions