[coreboot] GeodeLX RAM initialisation issue

[Nathan Williams]

Hi I am trying to sort out a RAM issue with coreboot on a motherboard we 
have designed at my work.

The board uses the AMD LX800 and CS5536 companion chipset.

I have been using coreboot-v3 and based my board port on the Alix 1.C 
code.  We have a SODIMM socket, so I used the initram.c from the 
amd/db800 code because it does SPD.

The symptoms are that sometimes a boot will die during disable_car() in
arch/x86/geodelx/stage1.c:

/* OK, here is the theory: we should be able to copy
          * the data back over itself, and the wbinvd should then
          * flush to memory. Let's see.
          */
         __asm__ __volatile__("cld; rep movsl" ::"D" (DCACHE_RAM_BASE), 
"S" (DCACHE_RAM_BASE), "c" (DCACHE_RAM_SIZE/4): "memory");
         __asm__ __volatile__ ("wbinvd\n");

Sometimes it boots fine and appears to be quite stable.  If I run 
software like mprime95 to "Torture Test" the system, it doesn't fail.

However, there is one strange phenomenon that I've noticed.  If I remove 
the RTC battery backup and Linux forces a fsck because the last boot 
time was in the future.  If Linux fixes a couple of errors and reboots 
automatically in 5 seconds, during the reboot it's almost guaranteed 
that coreboot will get stuck in disable_car().  I don't know if this is 
useful, or just a coincidence.  In my build I have also disabled the 
CMOS Option Table (CONFIG_OPTION_TABLE) in case something there might be 
causing the problem.

Initially I thought it was a hardware problem with our PCBs, but have 
tested with a bios chip from an AMD reference design board (EmbeddedBIOS 
v5.3) which booted Linux fine without any problems, so I have concluded 
that my problem must be something I'm doing (or not doing) in coreboot.

I have checked all the SPD values against the datasheet for the Hynix 
RAM chips (256MiB 333MHz).  I tried using the non-SPD method as in the 
Alix 1.C code and specified all the RAM parameters.  I have also tried 
to follow sdram_enable() and other functions in 
northbridge/amd/geodelx/raminit.c to check against the AMD LX databook's
section 6.1.3 BIOS Initialization Sequence, though I admit I could have 
easily missed something here.

I would be most grateful of any suggestions for helping me work out 
what's going wrong.

Regards,
Nathan