[Libreboot] GM45/GS45 internal reflash, Was: R400: Using GPIO33 to enable reflash

[Denis 'GNUtoo' Carikli]

On Fri, 1 Apr 2016 21:54:41 +0000 (UTC)
Joerg Albert <address@hidden> wrote:
> I wonder if the GPIO33 trick:
> 
> https://libreboot.org/docs/install/x200_external.html#gpio33)
> 
> would allow me to reflash libreboot without any external equipment
> (besides shorting two pads under the WWAN slot [R653] at boot time)?
I wonder if that could be used to reflash libreboot internally, from
the stock BIOS:
Assuming that we can disable the flash descriptor restrictions this
way, we might be able to reflash that flash descriptor, along with all
the flash not covered by the PR register.

On my X200T a PR protects what seem to be the bootblock.
So I wonder if there is a way to move the entry point of the boot
fimrware.

If my memory is good, the CPU jumps to the 0xFFFF0000 memory address.
On the flash, that's 64k before the end.
1) Is that covered by the PR registers.
2) If yes, can the BIOS partition be moved?

If either (1) or (2) is true we might be able to:
- Unlock the flash descriptor.
- reflash it, along with libreboot.
- boot on libreboot (without any PR registers set).
- reflash libreboot normally.

As a side note, on i945, we also had PR registers restrictions.
To get around it, the bucts[1] utility set the "top swap" field of the
BUCT register to swap flash zones, but this is now locked on the X200T
(GM45) default BIOS.

References:
-----------
[1]git://git.stuge.se/bucts.git

Denis.

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