On Thu, 2005-02-24 at 10:54 -0600, Chris Friesen wrote:

Not strictly linux related, but I thought someone might know the answer.

I've got a request from someone that wants to be able to flush the L2 on 
the 970.

The user manual has a procedure to do this, but it involves first 
flipping the cache to direct-mapped mode by setting SCOM register 
0x43000 bit 0x8000.  The only thing is, I can't find any linux code that 
ever touches the SCOM stuff, and the manual has no examples of *reading* 
from the SCOM area, just writing to it, so I'm not entirely sure how to 
do that.

A google search found the following snippet of darwin code:


lis r8,cFIR ; Get the Core FIR register address
ori r8,r8,0x8000 ; Set to read data
sync
mtspr scomc,r8 ; Request the Core FIR
mfspr r25,scomd ; Get the source
mfspr r8,scomc ; Get back the status (we just ignore it)
sync
isync	
			


This implies that bit 0x8000 needs to be set to specify a read command, 
and that we need to read the status after the read.  Does anyone know if 
this is in fact the case?

I think so. Also, there are some erratas with early 970's where the
stuff is shifted one bit. The Darwin source is a good reference for
that.

Also, in that code they make reference to early chip revisions that 
returned scom reads shifted by one bit.  Does anyone know which versions 
are affected?

I think all non-FX.

Ben.