On Fri, May 07, 2010 at 11:47:37AM +0200, Clemens Ladisch wrote:
Daniel Mack wrote:
The problem is again (summarized):
On 64bit machines, with 4GB or more, the allocated buffers for USB transfers might be beyond the 32bit boundary. In this case, the IOMMU should take care and install DMA bounce buffer to copy over the buffer before the transfer actually happens. The problem is, however, that this copy mechanism takes place when the URB with its associated buffer is submitted, not when the EHCI will actually do the transfer.
In the particular case of audio drivers, though, the contents of the buffers are likely to change after the submission. What we do here is that we map the audio stream buffers which are used by ALSA to the output URBs, so they're filled asychronously. Once the buffer is actually sent out on the bus, it is believed to contain proper audio date. If it doesn't, that's due to too tight audio timing or other problems. This breaks once buffers are magically bounced in the background.
At least the audio class and ua101 drivers don't do this and fill the buffers before they are submitted.
Gnaa, you're right. I _thought_ my code does it the way I described, but what I wrote is how I _wanted_ to do it, not how it's currently done. I have a plan to change this in the future.
So unfortunately, that doesn't explain it either. Sorry for the noise.
Daniel