83xx: Marking or Allocating Pages as Cache-Inhibited

[Ben Menchaca]

1.  BAT2 in linux is set to WIMG=0010, and covers all 64M
2.  PEX_DEVICE_CONTROL in PCI-E Config Space (0x54): 0x1020
3.  PEX_xDMA_CTRL is set to 0x00000401 at the initiation of the DMA.
4.  OWAR0 is set to 0xFFFFF005, so NSNP is 0.
5.  The DMA descriptor (randomly chosen when I hit a trigger...just ignore
the size...) contains 0002AFF3 at offset 0, so nosnoops are cleared.

Core is 400MHz, and CSB is 133MHz.

- Ben

On Thu, Mar 5, 2009 at 11:27 PM, Liu Dave-R63238 <DaveLiu at freescale.com>wrote:

> and what settings  is DMA description bit 3?
>
> > -----Original Message-----
> > From: linuxppc-dev-bounces+daveliu=freescale.com at ozlabs.org
> > [mailto:linuxppc-dev-bounces+daveliu <linuxppc-dev-bounces%2Bdaveliu>=
> freescale.com at ozlabs.org]
> >  On Behalf Of Liu Dave-R63238
> > Sent: Friday, March 06, 2009 1:22 PM
> > To: Ben Menchaca; linuxppc-dev at ozlabs.org
> > Subject: RE: 83xx: Marking or Allocating Pages as Cache-Inhibited
> >
> > 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 <linuxppc-dev-bounces%2Bdaveliu>=
> 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
> >
> >
> > _______________________________________________
> > Linuxppc-dev mailing list
> > Linuxppc-dev at ozlabs.org
> > https://ozlabs.org/mailman/listinfo/linuxppc-dev
> >
> >
>
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