Messages in this thread | | | Subject | Re: [RFC] ARM DMA mapping TODO, v1 | From | Benjamin Herrenschmidt <> | Date | Sat, 30 Apr 2011 08:51:54 +1000 |
| |
On Fri, 2011-04-29 at 12:56 +0100, Alan Cox wrote: > > I believe that the PC graphics cards that have noncoherent DMA mappings > > are all of the unified memory (integrated into the northbridge) kind, > > so they are not on the same host bridge as all regular PCI devices, > > even if they appear as a PCI device. > > The AGP GART is not coherent on a lot of systems - not necessarily > unified memory though, it can be a plug in AGP card too. > The GART is basically an IOMMU (and indeed in the later AMD case used > exactly as that)
Right. Actually there's also the ability for PCIe devices to set a "no snoop" bit on transactions and thus behave in a non-coherent manner. Hopefully most sane PHBs ignore that bit ...
Cheers, Ben.
| |