x86: Zero SMBIOS region before writing tables

Clear the SMBIOS region before writing SMBIOS tables.

On librem_mini and librem_mini_v2, CBMEM allocations are offset by 4K
for reboots relative to the cold boot.  This means the unused SMBIOS
region could contain the first 4K of the ACPI tables from the last boot
(including the signature), which prevents Linux from booting.

The CBMEM 4K offset appears to be due to FSP allocating memory
differently between cold boot and reboot, this appears to be normal and
causes the CBMEM base address to change.

It is not clear why Linux examines an ACPI signature found in this
region, but boot logs over serial confirm that it sees the corrupt
table.  The table is supposed to be found just below 1M, and kernel
source appears to look in this region, but it is definitely finding the
corrupt table in CBMEM.

Normal cold boot:
  [    0.008615] ACPI: RSDP 0x00000000000F6190 000024 (v02 COREv4)
  [    0.008619] ACPI: XSDT 0x0000000099B480E0 00005C (v01 COREv4 COREBOOT 00000000 CORE 20220331)
  [    0.008624] ACPI: FACP 0x0000000099B4A2A0 000114 (v06 COREv4 COREBOOT 00000000 CORE 20220331)
  [    0.008634] ACPI: DSDT 0x0000000099B48280 00201F (v02 COREv4 COREBOOT 20110725 INTL 20220331)
  ...

Reboot with corrupt table:
  [    0.008820] ACPI: RSDP 0x00000000000F6190 000024 (v02 COREv4)
  [    0.008823] ACPI: XSDT 0x0000000099B480E0 00005C (v01 COREv4 COREBOOT 00000000 CORE 20220331)
  [    0.008828] ACPI: ???G 0x0000000099B4A2A0 20002001 (v00 ?G?$            47020100 ?,   47020100)
  [    0.008831] ACPI: �y   0x0000000099B4A3C0 54523882 (v67 ?_HID? A�?      65520D4E al T 20656D69)
  ...

There are no specific errors but it returns to the firmware soon after,
presumably due to a fault.  This appears to be so early in the boot
that panic=0 on the kernel command line has no effect.

Test: build/boot Librem Mini, Librem Mini v2 and reboot.

Change-Id: Ia20d0b30160e89e8d96add34d7e0e881f070ec61
Signed-off-by: Jonathon Hall <jonathon.hall@puri.sm>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/66377
Reviewed-by: Matt DeVillier <matt.devillier@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>

0 files changed, 0 insertions, 0 deletions