On Wednesday 12 November 2014 09:18:59 Konrad Rzeszutek Wilk wrote: > On Wed, Nov 12, 2014 at 01:39:05PM +0100, Thierry Reding wrote: > > From: Thierry Reding <treding@xxxxxxxxxx> > > > > dma_alloc_coherent() returns a kernel virtual address that is part of > > the linear range. Passing such an address to virt_to_page() is illegal > > on non-coherent architectures. This causes the kernel to oops on 64-bit > > ARM because the struct page * obtained from virt_to_page() points to > > unmapped memory. > > Oh! That is not good! > I think what Thierry meant is that the returned pointer is /not/ in the linear range. > > Until that time, this temporary fix will allow TTM to work on 32-bit > > and 64-bit ARM as well, provided that no IOMMU translations are enabled > > for the GPU. > > Is there a way to query the 'struct device' to see if the IOMMU translation > is enabled/disabled for said device? > > Now your patch looks to get the 'struct page' by doing some form of > translation. Could you explain to me which type of memory have a 'struct page' > and which ones do not ? > > It is OK if you explain this in nauseating details Basically there are two types of memory that have a struct page: - directly mapped cacheable memory, i.e. anything that can be accessed through a kernel pointer without having to go though ioremap/vmalloc/... - highmem pages on 32-bit system. On noncoherent ARM systems, dma_alloc_coherent will return memory that is was unmapped from the linear range to avoid having both cacheable and noncachable mappings for the same page. Arnd _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
