On Mon, 22 Mar 2010, Hemanth V wrote: > > On Fri, 19 Mar 2010, Nicolas Pitre wrote: > > > >> A highmem page can have 2 states: virtually mapped in the pkmap area, or > >> not mapped at all. When it is mapped then page_address() returns a > >> valid virtual address for it. In that case the cache for that mapping > >> can be valid, even dirty. So the DMA API will perform cache handling > >> before/after the DMA operation. > >> > >> However, before the page is unmapped, the VIVT cache has to be flushed > >> for that page. This is why the DMA code currently doesn't bother doing > >> any L1 cache handling when a highmem page is not mapped -- the cache > >> just can't refer to such a page. > >> > >> But on ARMv6 this is different. The L1 cache is VIPT and it therefore > >> doesn't have to be flushed as often as a VIVT cache. Still, as far as I > >> know, the highmem code currently always flush any page to be unmapped. > >> But somewhere somehow an unmapped highmem page becomes subject to DMA > >> and apparently can still be L1 cached. But the DMA code doesn't flush > >> its cache due to the page not being mapped and then problems occur. > > > > And here's a patch to test that hypothesis. With this patch, all the > > issues with highmem on my ARMv6 system are gone. > > > > Modified version of this patch also solves the problem for 2.6.32-rc7 > on ARM v7. OK thanks for testing. I'll work on a proper patch now. Nicolas -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
