Messages in this thread | | | Date | Tue, 11 May 2010 23:38:35 +0900 | Subject | Re: [alsa-devel] USB transfer_buffer allocations on 64bit systems | From | FUJITA Tomonori <> |
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On Tue, 11 May 2010 10:24:40 -0400 Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> wrote:
> > > > Either the data isn't getting written to the buffer correctly or else > > > > the buffer isn't getting sent to the device correctly. Can anybody > > > > suggest a means of determining which is the case? > > > > > > I can't say anything about this log that including only DMA addresses. > > > I'm not familiar with how the USB core does DMA stuff. And the USB > > > stack design that the USB core does DMA stuff (allocating, mappings, > > > etc) makes debugging DMA issues really difficult. > > > > The DMA stuff is simple enough in this case. The urb->transfer_buffer > > address is passed to dma_map_single(), and the DMA address it returns > > is stored in urb->transfer_dma. Those are the two values printed out > > by the debugging patch. > > Is that address (urb->transfer_dma) the same as 'virt_to_phys(urb->transfer_buffer)' > (if not, then SWIOTLB is being utilized) and is the dma_sync_* done on the > urb->transfer_dma (to properly sync the data from the SWIOTLB to the > transfer_buffer) before you start using the urb->transfer_buffer?
Or calling dma_unmap_single.
Can you tell me all the exact process of DMA that the usb core and the driver do?
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