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    SubjectRe: [PATCH v5 12/13] swiotlb-xen: use xen_alloc/free_coherent_pages
    On Fri, 30 Aug 2013, Konrad Rzeszutek Wilk wrote:
    > On Thu, Aug 29, 2013 at 07:32:33PM +0100, Stefano Stabellini wrote:
    > > Use xen_alloc_coherent_pages and xen_free_coherent_pages to allocate or
    > > free coherent pages.
    > >
    > > We need to be careful handling the pointer returned by
    > > xen_alloc_coherent_pages, because on ARM the pointer is not equal to
    > > phys_to_virt(*dma_handle). In fact virt_to_phys on the returned pointer
    > > doesn't return a valid physical address.
    >
    > Why is it called 'virt_to_phys'? What does it return then?

    virt_to_phys only works for kernel direct mapped RAM memory.
    In this case the virtual address could be an ioremap address, therefore
    passing it to virt_to_phys would give you another physical address that
    doesn't correspond to it.


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