[coreboot] [PATCH] Add support for Asus M4A785-M, with build instructions

Juhana Helovuo juhe at iki.fi
Mon Sep 13 19:26:38 CEST 2010

On Mon, 2010-09-13 at 10:29 -0600, Myles Watson wrote:

> The problem seems to be that the mainboard code gets its information
> on the size of memory from TOP_MEM, but that hasn't been set correctly
> with respect to the PCI resources yet.
> m4a785m_enable, TOP MEM: msr.lo = 0xe0000000, msr.hi = 0x00000000
> m4a785m_enable, TOP MEM2: msr2.lo = 0xa0000000, msr2.hi = 0x00000001
> m4a785m_enable: uma size 0x10000000, memory start 0xd0000000
> ...
> Root Device assign_resources, bus 0 link: 0
>  split: 64K table at =cfff0000
> 0: mmio_basek=00300000, basek=00400000, limitk=00680000
> Adding UMA memory area
> So even though there are PCI resources located at 0xc0000000, RAM gets
> used for UMA at 0xd0000000 and tables get placed at 0xcfff0000.
> You could test that theory by hard coding the top mem logic in mainboard.c.
> Because the mainboard device is at the root of the tree, the
> northbridge initialization hasn't been done yet, so the values it
> wants haven't been calculated.

I tried with the following:

	/* TOP_MEM: the top of DRAM below 4G */
	msr = rdmsr(TOP_MEM);
	//hardwire this for testing
	if (msr.lo > 0x80000000) { msr.lo = 0x80000000; }

This code manages to set UMA to a lower address, but the effect is the
same as with hardwiring UMA address. Boot proceeds past VGA BIOS, but
results in random crashes and reboots.

Or did you mean some other hardwiring? 

Since variable "msr" here is local to the routine, I don't see how it
could have effect on anything else but the UMA location and size. The
value read from TOP_MEM2 isn't even used for anything but printing.

Best regards,
Juhana Helovuo

More information about the coreboot mailing list