Re: [Qemu-ppc] [PATCH 2/2] tcg/ppc*: Move cache initialization to ppc specific code

[Benjamin Herrenschmidt]

> Not doing it sometimes invokes crash penalties for us. :-)
> 
> We could add some way to skip the invalidation if we know the host is an
> implementation that doesn't need it, possibly depending on the context
> (is it just DMA he wants to avoid doing this on[1], or do their chips
> have a fully coherent icache?), but IMHO functional correctness should
> come first.
> 
> -Scott
> 
> [1] In which case we need to figure out how to tell at that point
> whether it was DMA, preferably by something less hackish than saying,
> "This function is used for DMA and breakpoints.  Breakpoints are 4
> bytes, and flushing on a 4-byte DMA isn't as painful as larger DMAs."

AT_HWCAP will tell you, look for PPC_FEATURE_ICACHE_SNOOP, in this case
all you need is sync, one icbi, isync (the arch documents the sequence
iirc).

Cheers,
Ben.