[coreboot] RFC: Changing CBMEM console to run as a persistent ring-buffer

[Vladimir 'phcoder' Serbinenko]

On Tue, Apr 25, 2017, 20:15 Julius Werner <jwerner at chromium.org> wrote:

> I'm very concerned with compatibility. You can't guarantee that coreboot
>> and payload match. And in case of mismatch you get a memory corruption that
>> is very hard to trace. Can we please change signature of cbmem entry?
>
>
> I would rather allow older implementations to continue working as best as
> possible. Changing the signature would mean that an old payload (or 'cbmem'
> command line tool, etc.) couldn't interoperate at all with the console. The
> changes I made are as backwards-compatible as possible: in many cases (e.g.
> before the console rolled over once) the old payload will continue working
> just fine. If the console did roll over, the old payload can no longer
> append lines and may print existing contents out of order. It will never
> access invalid memory, though. (You may have been worried about bit 31 I'm
> setting in the "cursor" field, but all existing implementations were
> already required to check (cursor < size) before trusting the cursor to be
> accessible since the old console would continue counting characters even
> after the buffer filled up.)
>
Did you check that all implementations use unsigned?

>
>
>> You mentioned having trouble building GRUB. Can you detail those?
>> What do you mean by not having hardware supported by grub-coreboot?
>> Grub-coreboot should work on all coreboot-supported boards.
>>
>
> I am able to build it, I just had to figure out how and install some
> dependencies. But I tried booting it on an HP Chromebook 14 2013 (falco)
> and it doesn't seem to recognize my keyboard
>
Is it PS2 or USB? Is at_keyboard included in the payload?

> and will reboot a few seconds after displaying the GRUB console. (Most of
> the devices I have are ARM unfortunately, which I'm assuming it doesn't
> support since all the coreboot code is in i386 directories?
>
Arm is in separate branch due to freeze.

>  even if it did, it probably wouldn't have a keyboard driver for them
> either. I assume there's no way to make it run over the UART instead?)
>
terminal_input serial_com0
terminal_output serial_com0
In etc/grub.cfg

Possibly the problem is that some module hangs. Can you try minimal GRUB
without non-essential modules?

>
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