On 05/16/2013 01:19 PM, Sarah Sharp wrote:
On Thu, May 16, 2013 at 10:11:00AM -0400, Alan Stern wrote:
On Wed, 15 May 2013, Sarah Sharp wrote:
If you're using 64-bit DMA then you almost certainly do want to call
dma_set_coherent_mask(). On the plus side, it is guaranteed that if
dma_set_mask() succeeds with a particular mask value then
dma_set_coherent_mask() for the same mask value will also succeed.
So we need to call both dma_set_coherent_mask() and dma_set_mask()? Or
just dma_set_coherent_mask()?
It depends on what kind of DMA transfers you're going to do. For
streaming transfers (the ones that use dma_map_single() or
dma_map_sg(), for example), you need to call dma_set_mask(). For
coherent transfers (the ones that use dma_alloc_coherent() or
dma_pool_create()), you need to call dma_set_coherent_mask().
If you want to do both kinds of transfers then you need to call both
routines.
I think we need the host to be able to do DMA to URB buffers that are
mapped with dma_map_single() or dma_map_sg(), since that's what
usb_hcd_submit_urb() uses. So the driver needs to call dma_set_mask(),
which it does.
The xHCI endpoint rings are allocated from DMA pools, so we need to
call dma_set_coherent_mask() as well. Missing that call explains why
I've never seen 64-bit endpoint rings, but I have seen 64-bit URB buffer
pointers.
Correct. Otherwise, that DMA is going through the (more limited 64MB) bounce
buffer
which is allocated out of low memory since... a device can't do 64-bit
addressing;
Ksenia, do you want to add code to add the call to
dma_set_coherent_mask() in those two places in xhci_gen_setup()? As I
mentioned, let's add this function call first, and then have a separate
commit refactor the copy-paste code into a new function.
Again, thanks for catching this and asking questions!
Sarah Sharp
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