83xx: Marking or Allocating Pages as Cache-Inhibited

[Liu Dave-R63238]

Did you enable the snoop bit at PEX_WDMA_CTRL[SNOOP]
and PEX_RDMA_CTRL[SNOOP]?

What is the freq settings? CORE/CSB bus.

Thanks, Dave

________________________________

	From: linuxppc-dev-bounces+daveliu=freescale.com at ozlabs.org
[mailto:linuxppc-dev-bounces+daveliu=freescale.com at ozlabs.org] On Behalf
Of Ben Menchaca
	Sent: Friday, March 06, 2009 12:33 PM
	To: linuxppc-dev at ozlabs.org
	Subject: 83xx: Marking or Allocating Pages as Cache-Inhibited
	
	
	I am working on a Freescale 8314e design, and the embedded
device is configured as a PCI-e endpoint running a 2.6.27-5 kernel.  For
context, we have written a kernel module which, among other things, uses
the RDMA/WDMA engine in the PCI-e IP block.  On the host side, these
DMAs are coherent.  However, on the embedded side, things are quite a
bit less rosy; we must manually flush/invalidate cache lines for
WDMA/RDMAs to occur successfully.  After speaking with (several) FAEs at
Freescale, we believe there is a configuration issue that is the cause,
but we have yet to have anyone successfully point to it.  
	
	Disabling the data cache altogether resolves the issue entirely,
but of course, also completely tanks performance.  As a temporary
workaround, I would like to simply mark the pages (obtained currently
via dma_alloc_coherent) involved as cache-inhibited.  I have attempted
to do this via some snippets remaining in fec.c (va_to_pte, uncache_pte
to set _PAGE_NO_CACHE, flush_tlb_page, then unmap_pte), but this is
almost certainly braindead; va_to_pte is not a part of the 83xx source,
as far as I can tell; 8xx only.
	
	A quick pointer in the correct direction for marking pages as
cache-inhibited on a 2.6.27-5 kernel would be appreciated, or if my
approach to a workaround is flawed, a pointer to the correct way would
be great.
	
	Ben Menchaca