cpu/x86/mtrr: Fix _FROM_4G_TOP() macro

This macro was unnecessarily complex. Trying to avoid an overflow
for unknown reasons, and instead shifted the result into the sign
bit in C. Using a plain number literal that forces C to use an
adequate integer type seems to be safe. We start with 0xffffffff,
subtract `x` and add 1 again. Turned out to be a common pattern
and can't overflow for any positive 32-bit `x`.

Change-Id: Ibb0c5b88a6e42d3ef2990196a5b99ace90ea8ee8
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/31322
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>

0 files changed, 0 insertions, 0 deletions