[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v5 12/13] swiotlb-xen: use xen_alloc/free_coherent_pages
On Thu, Sep 05, 2013 at 05:50:45PM +0100, Stefano Stabellini wrote: > 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. Ah, so very much ARM (and in some way SPARC) specific. I think you need add some comments in the code (And git commit) to explain this. Thank you. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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