Socflash says the bmc is write protected.

[Andrew Jeffery]

On Tue, 27 Aug 2019, at 04:16, James Mihm wrote:
> The best that can be done with the AST2500 is to disable the bridges 
> very early in the reset handler and in a ROM'd bootloader. This has 
> been mitigated in the AST2600 with an option to permanently disable the 
> bridges.

For the 2500 you can also do it before the first instruction is executed on
the ARM core by taking advantage of the firmware strapping function. This
is about a small a window as you're going to get though.

OpenBMC's approach of doing it early in u-boot is the pragmatic approach
as you can read/modify/write the registers, which isn't possible via the
firmware strapping method.

Andrew