[coreboot] Question regarding two registers on the LPC bridge in AMD Hudson

Wei Hu wei at aristanetworks.com
Sat Aug 3 10:27:38 CEST 2013

On Sat, Aug 3, 2013 at 1:09 AM, Wei Hu <wei at aristanetworks.com> wrote:
> Hi,
> I see hudson_enable_rom() in southbridge/amd/agesa/hudson/bootblock.c
> enables LPC ROM decoding and sets up ROM address range 2 to be
> identical to ROM size. In particular I'm referring to the two
> registers at 0x48 and 0x6c.
> However, when I boot into Linux I found the LPC ROM Range Port Enable
> bits were cleared, which is fine I suppose since the boot rom is off
> SPI instead of LPC? And the ROM Address Range 2 was set to start from
> 0xff00_0000. I think it should start from 0xffc0_0000 instead since
> the flash size is 4MB.
> I'm curious what else would bother to write to those registers? Also,
> what register on AMD chip is used to cancel the legacy BIOS mapping at
> 1MB? On Intel northbridge there are the PAM (programmable attribute
> map) registers.

On AMD we control the access through the RdDram/WrDram bits in the
fixed MTRRs. With bit set, access goes to RAM, otherwise gets passed
down to southbridge. Is it correct?

> Thanks,
> Wei

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