[LinuxBIOS] Question about raminit.c

[joe at smittys.pointclark.net]

If the SPD register settings can be read through the SMBUS than it  
seems a little silly to set any of the memory controller registers  
first. Exactly my point Corey, why do anything twice if you don't have  
to. raminit.c seems to set the memory controller registers first,  
detect SPD, calculate, and re-set the memory controller registers  
again. If we cut to the chase and just detect SPD,calculate, and set  
the memory controller registers, it could speed things up alot more.  
:) Thoughts?

Thanks - Joe

Quoting Corey Osgood <corey_osgood at verizon.net>:

> joe at smittys.pointclark.net wrote:
>> Is SPD detection done though the memory controller or through the
>> superIO via the SMBUS (i2c)?
>>
>
> Through SMBus, on the southbridge. I'm not positive about Intel's setup,
> but with Via you have to first set up a couple registers on the
> southbridge to set the SMBus port address, then stick in a few functions
> for reading spd data (see smbus_read_byte and smbus_enable in
> southbridge/<model>/early_smbus.c). Here's some nice writeups on SPD:
>
> DDR2:  http://www.simmtester.com/page/news/showpubnews.asp?num=139
> DDR:   http://www.simmtester.com/page/news/showpubnews.asp?num=101
> SDRAM: http://www.intel.com/design/chipsets/memory/spdsd12a.pdf (sorry,
> no nice simple writeup available, but check out the other ones for
> pointers. This also isn't the best datasheet on it, but I'm too lazy to
> go diving into the JEDEC site again)
>
> The picture on the first two links shows the SPD rom on a memory module,
> note it's not part of the actual memory and connects to pins which
> connect to the southbridge, so it can be read before ram init ever
> occurs, or even during ram init, without disturbing things. The BIOS
> Porting Guides I've read usually recommend to do ram init with safe
> values (minimum size for all banks, extremely loose timings) before
> attempting to read the spd, but most factory BIOSs don't have the power
> of cache-as-ram :D Since ram init takes only but a few milliseconds, you
> can do it that way if you want, but my way of thinking is why do
> anything twice if you don't have to?
>
> -Corey
>
>