[coreboot] VIA C7 on BCom Winnet P680 - L1/L2 cache very slow

Corey Osgood corey.osgood at gmail.com
Sun Oct 6 08:43:00 CEST 2013

After sending the last message, I've done a little more debugging and
dumped cr0, and also checked the C7 FCR, everything indicates the cache is
properly enabled and not in NoWriteThrough mode, although I have very
little C7 specific information and none of it relating to cache.

So, I'm now looking elsewhere, and at the moment I'm looking at MTRRs. All
the fixed MTRRs, under coreboot, are 0'd out, and variable are all type 6
(WB?), as can be seen in the attached boot log. Here's the way the stock
BIOS sets them up:

# IA32_MTRR_FIX64K_00000 0x00000250 = 0x0606060606060606
# IA32_MTRR_FIX16K_80000 0x00000258 = 0x0606060606060606
# IA32_MTRR_FIX16K_A0000 0x00000259 = 0x0000000000000000
# IA32_MTRR_FIX4K_C0000 0x00000268 = 0x0505050505050505
# IA32_MTRR_FIX4K_C8000 0x00000269 = 0x0000000505050505
# IA32_MTRR_FIX4K_D0000 0x0000026a = 0x0000000000000000
# IA32_MTRR_FIX4K_D8000 0x0000026b = 0x0000000000000000
# IA32_MTRR_FIX4K_E0000 0x0000026c = 0x0000000000000000
# IA32_MTRR_FIX4K_E8000 0x0000026d = 0x0000000000000000
# IA32_MTRR_FIX4K_F0000 0x0000026e = 0x0404040404040404
# IA32_MTRR_FIX4K_F8000 0x0000026f = 0x0404040404040400
root at khan:~/coreboot/util/msrtool# cat
reg00: base=0x000000000 (    0MB), size= 1024MB, count=1:
reg01: base=0x03e000000 (  992MB), size=   32MB, count=1:
reg02: base=0x0f8000000 ( 3968MB), size=   32MB, count=2:
reg03: base=0x03df00000 (  991MB), size=    1MB, count=1:
reg04: base=0x0f4000000 ( 3904MB), size=   32MB, count=1: write-combining

I'm frankly not sure if I'm on the right track or not, I've done some work
porting chipsets but very little with the CPU itself. Any help would be
greatly appreciated, I was hoping this project was "just" writing IRQ and
ACPI tables.


On Sat, Oct 5, 2013 at 6:03 AM, Corey Osgood <corey.osgood at gmail.com> wrote:

> I'm working on fixing up the BCom WinNet P680 port, which is a Via C7 CPU
> and CN700/VT8237R chipset. I've got it running enough to boot a Memtest86
> payload, but it's very slow. The L1 and L2 cache are reported as running at
> 11-12MB/s by Memtest, which is much slower then they're reported as running
> in the stock BIOS. This makes any further testing impractical, as it takes
> ages load a kernel+initrd. Any suggestions on how to fix this, or where to
> look?
> Thanks,
> Corey
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