lkml.org 
[lkml]   [2010]   [May]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [alsa-devel] USB transfer_buffer allocations on 64bit systems
    On Tue, 11 May 2010, FUJITA Tomonori wrote:

    > 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?

    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



    \
     
     \ /
      Last update: 2010-05-12 10:35    [W:0.020 / U:30.724 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site