[coreboot] C720 swapparoo

[Duncan Laurie]

On Wed, Jan 29, 2014 at 10:55 AM, John Lewis <jlewis at johnlewis.ie> wrote:
> Dear List,
>
> If I dd the contents of the RW_LEGACY slot into the WP_RO slot on the stock
> c720 firmware, will it a) Still work and b) then boot into SeaBIOS by
> default? :)
>

Unfortunately it is not that simple since SeaBIOS does not have the
hardware initialization bits needed to bring up the device.

If you want to boot SeaBIOS by default and you have unlocked the SPI
flash write protection you can set flags in the (write protected) "GBB"
flash region that will make it boot legacy mode by default.

In Chrome OS there is a script called set_gbb_flags.sh that will do
this for you.  Run the script with no arguments to get a list of
possible flags and then to enable short dev mode screen (1 second
timeout) followed by default legacy mode boot you could use these
flags:

  GBB_FLAG_DEV_SCREEN_SHORT_DELAY     0x00000001
  GBB_FLAG_FORCE_DEV_SWITCH_ON        0x00000008
  GBB_FLAG_FORCE_DEV_BOOT_LEGACY      0x00000080
  GBB_FLAG_DEFAULT_DEV_BOOT_LEGACY    0x00000400

set_gbb_flags.sh 0x489

Of course you could also replace the payload with SeaBIOS directly if
you are so inclined.  This is just a way to enable default legacy mode
without having to modify the underlying firmware.

-duncan