On Tue, 11 May 2010, FUJITA Tomonori wrote: > On Tue, 11 May 2010 10:24:40 -0400 > Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> 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? 1. The audio driver stores data in urb->transfer_buffer. 2. The audio driver calls usb_submit_urb(urb). 3. The USB core does urb->transfer_dma = dma_map_single(controller, urb->transfer_buffer, urb->transfer_buffer_length, DMA_TO_DEVICE); 4. The host controller driver tells the hardware to carry out the data transfer. 5. When the hardware says the transfer is finished, the USB core does dma_unmap_single(controller, urb->transfer_dma, urb->transfer_buffer_length, DMA_TO_DEVICE); 6. The audio driver's completion handler is called: (urb->complete)(urb); Alan Stern _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
