Messages in this thread | | | Date | Tue, 9 Mar 2010 15:45:54 +0800 | Subject | Re: DMA using data buffer vmapped in kernel space | From | Lin Mac <> |
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2010/3/7 Russell King - ARM Linux <linux@arm.linux.org.uk>: > On Sat, Mar 06, 2010 at 02:07:12PM +0100, Thomas Koeller wrote: >> Am Donnerstag, 4. März 2010 22:36:34 schrieb Russell King - ARM Linux: >> > Cache maintainence is done using virtual addresses for L1, and >> > physical addresses for L2. There's the need for virtual addresses >> > to be translatable to physical addresses, which is only true for >> > the kernel direct mapped region (pages between PAGE_OFFSET and >> > high_memory). >> >> Isn't the mapping created by vmap() sufficient for the virt/phys >> translation? In which way is this case different from a buffer >> passed in from user space, where the constituent pages are not >> in the directly mapped kernel region either? > > No different. > > The requirement is that dma_map_single() is passed a virtual address > in the kernel direct-mapped memory region, which is translatable using > virt_to_phys() and friends. I had encounter a similiar problem and I simply allocated a new buffer, copy the data, then DMA. It seems slow and stupid.
I'm wondering wether could I translate the vmap virt to phys(don't know how to yet), then use phys_to_virt to get the virt in direct-mapped memory region?
Is there other possible ways?
> Anything which requires a page table lookup to obtain the physical > address is just not acceptable - that requires taking locks and other > messy things, plus is grossly inefficient.
Best Regards, Mac Lin -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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