On Wed, 2009-01-28 at 13:34 +0100, Thomas Hellström wrote:
> Dave Airlie wrote:
> > On Wed, 28 Jan 2009, Shunichi Fuji wrote:
> >
> >> BTW using Write-Combining for ring-buffer is safe?
> >> I afraid a bit that miss ordered.
> >>
> >
> > Yes it should be fine, write combining shouldn't re-order,
> > and its been write combined using an mtrr for years.
> >
> >
> Actually, I think it may re-order, so WC buffers need to be flushed with
> an mb() before
> updating registers or pointers that depend on data being present in memory.
Yeah, we were over this years ago. :) The radeon COMMIT_RING() macro
takes care of this:
/* Flush writes to ring */ \
DRM_MEMORYBARRIER(); \
GET_RING_HEAD( dev_priv ); \
RADEON_WRITE( RADEON_CP_RB_WPTR, dev_priv->ring.tail ); \
/* read from PCI bus to ensure correct posting */ \
RADEON_READ( RADEON_CP_RB_RPTR ); \
--
Earthling Michel Dänzer | http://www.vmware.com
Libre software enthusiast | Debian, X and DRI developer
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