acpi/acpigen: add comment about byte 0 in acpigen_resource_*word

Since it's not obvious, add comments to acpigen_resource_word,
acpigen_resource_dword and acpigen_resource_qword to clarify out what
the magic number in byte 0 means. The most significant bit of byte 0
indicates if it is a small or large resource data type. In the case of
the MSB being 0, it's a small resource data type (aka type 0), and the
other bits encode bit the type and size of the item; if the MSB is 1,
it's a large resource data type (aka type 1), and the other bits just
encode the type and there are two separate bytes to encode the size.
Beware that the large resource's data type values in the ACPI
specification don't include the MSB that's set, but only the 7 lower
bits.

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Change-Id: Ia6a6c9fb1bcde232122bb5899b9a0983ef48e12b
Reviewed-on: https://review.coreboot.org/c/coreboot/+/75158
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tim Wawrzynczak <inforichland@gmail.com>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>

0 files changed, 0 insertions, 0 deletions