[coreboot] Early debugging

[Kyösti Mälkki]

On Mon, Dec 4, 2017 at 2:44 PM, Gergely Kiss <mail.gery at gmail.com> wrote:
> Hi,
>
> I'm working on porting Coreboot to the ASUS AM1I-A motherboard and I'm a bit
> stuck.
>
> I could successfully build Coreboot but after flashing the ROM, my board
> looks to be bricked...
>
> Once powering on the board, the CPU fan spins up but then nothing happens, I
> can't see any output on the serial console (the connection was tested prior
> to flashing by running a getty on the COM port and it was working fine).
>

Common errors: Forgetting to use correct super-IO config base address
(0x2e vs 0x4e) and not providing 48MHz reference clock for the uart
baudrate divisor. AMD hardware often uses configurable GPIO pins for
this purpose, the code copied from biostar/am1ml may not be right for
asus/am1l-a.

You can dump those GPIO configurations eg. with iotools or even dd
from /dev/mem. Related datasheets for the Kabini family should be
available without NDAs.

> The board is not fried as I can load back the vendor firmware and it boots
> up absolutely fine.
>
> I'd like to find out why Coreboot would not start but don't know what tool
> would be the most suitable for debugging.
>
> The chipset and the CPU is already supported by Coreboot but the SuperIO
> chip is not. It looks to me the serial interfaces of ITE chips work the same
> for all models so I believe using the common code for ITE SIO chips should
> work but I'm unsure (no datasheet available).

AM1 socket support is a hack anyways, grep for
FORCE_AM1_SOCKET_SUPPORT. Your mileage may vary.

It's not uncommon that PNP LDNs for the UARTs change within one vendor.
Did you run util/superiotool and dump SIO settings from vendor boot?

>
> Shall I use a PCIe serial interface card or rather try EHCI debugging? I'm
> afraid in case the boot process halts at some early stage (like before
> romstage) then I won't see any useful output using any of those.
>

EHCI debug should be fine nowadays with AGESA, still not my first
choice here for you.
PCIe serial cards are untested, probably do not work early enough to
be useful for you.
Traditional serial port debug will also be silent before romstage...

> Using a POST card would be a better approach I think but my board has a
> single PCIe 4x slot which seems to be unsupported by POST cards I could find
> on the web (except one from a Chinese vendor but it costs about $1k which is
> way too expensive).

Those mini-PCI-e POST cards with 7-seg displays are about 4 USD and
your mainboard TPM connector seems to carry the required LPC signals.
Remember to enable and route POSTs to LPC (kconfig POST_DEVICE_LPC).

>
> Here's my WIP code for reference:
>
> https://github.com/kissg1988/coreboot/tree/master/src/mainboard/asus/am1i-a
>
> Any idea how to proceed?
>

Get one of those POST cards, try to show vendor/device ID registers
from superio on the 7-seg display.

> Thanks,
> Gergely
>
>

HTH,
Kyösti

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