> 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. Thanks Hemanth -- 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
