[PATCH] ppc32/64: Map prefetchable PCI without guarded bit

Jesse Barnes jbarnes at engr.sgi.com
Fri Mar 25 03:54:45 EST 2005

On Wednesday, March 23, 2005 10:24 pm, Benjamin Herrenschmidt wrote:
> While experimenting with framebuffer access performances, we noticed a
> very significant improvement in write access to it when not setting
> the "guarded" bit on the MMU mappings. This bit basically says that
> reads and writes won't have side effects (it allows speculation). It
> appears that it also disables write combining.

Doesn't pgprot_writecombine imply non-guarded, so can't you use it instead?  
Either way, you'll probably want to fix fbmem.c as well and turn off 

Maybe it's time for a more generic call to support this stuff, both for 
in-kernel mappings and ones that we export to userspace.


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