Messages in this thread | | | Date | Fri, 29 Apr 2011 14:06:12 +0200 | From | Thomas Hellstrom <> | Subject | Re: [Linaro-mm-sig] [RFC] ARM DMA mapping TODO, v1 |
| |
On 04/29/2011 01:26 PM, Arnd Bergmann wrote: > On Thursday 28 April 2011, Benjamin Herrenschmidt wrote: > >>>> For PCI you can have the flag propagate from the PHB down, for busses >>>> without a bus type (platform) then whoever instanciate them (the >>>> platform code) can set that appropriately. >>>> >>> How can you do that when it changes mid-bus heirarchy? I'm thinking >>> of the situation where the DRM stuff is on a child bus below the >>> root bus, and the root bus has DMA coherent devices on it but the DRM >>> stuff doesn't. >>> >> But that's not PCI right ? IE. with PCI, coherency is a property of the >> PHB... >> > That is my understanding at least, but I'd like to have a confirmation > from the DRM folks. > > 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. >
I think Jerome has mentioned at one point that the Radeon graphics cards support non-coherent mappings.
Fwiw, the PowerVR SGX MMU also supports this mode of operation, although it being functional I guess depends on the system implementation.
/Thomas
> Arnd > > _______________________________________________ > Linaro-mm-sig mailing list > Linaro-mm-sig@lists.linaro.org > http://lists.linaro.org/mailman/listinfo/linaro-mm-sig >
| |