29 Apr
2011
29 Apr
'11
10:53 p.m.
On Fri, 2011-04-29 at 14:06 +0200, Thomas Hellstrom wrote:
I think Jerome has mentioned at one point that the Radeon graphics cards support non-coherent mappings.
If the card is PCI/PCI-X/PCIe then coherency is not its business, it's the business of the host bridge. However, on PCIe at least, the card can indeed set a "no snoop" attribute on DMA transactions to request "no coherency". At least the systems have the latitude to just ignore that bit (like we do on all ppc afaik) :-)
Fwiw, the PowerVR SGX MMU also supports this mode of operation, although it being functional I guess depends on the system implementation.
Right, it's not a GPU thing, it's really a system design thing.
Cheers, Ben.