[alsa-devel] USB transfer_buffer allocations on 64bit systems
fujita.tomonori at lab.ntt.co.jp
Tue May 11 17:34:27 CEST 2010
On Tue, 11 May 2010 11:04:55 -0400 (EDT)
Alan Stern <stern at rowland.harvard.edu> wrote:
> On Tue, 11 May 2010, FUJITA Tomonori wrote:
> > On Tue, 11 May 2010 10:24:40 -0400
> > Konrad Rzeszutek Wilk <konrad.wilk at 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.
How urb->transfer_buffer is allocated?
> 2. The audio driver calls usb_submit_urb(urb).
> 3. The USB core does
> urb->transfer_dma = dma_map_single(controller,
The mapping error is checked via dma_mapping_error? Even if an mapping
error happens, no data corruption happens due to that (needs
something like retrying the request)?
> 4. The host controller driver tells the hardware to carry out the data
> 5. When the hardware says the transfer is finished, the USB core does
> 6. The audio driver's completion handler is called:
The driver does only DMA_TO_DEVICE? Or you see DMA problems only with
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