On Fri, 9 Apr 2010, Pedro Ribeiro wrote: > On 8 April 2010 17:57, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > On Thu, 8 Apr 2010, Daniel Mack wrote: > > > >> > > AFAIK, the driver shouldn't have to worry about this at all. When the > >> > > buffer gets DMA-mapped for the controller, the DMA mapping code should > >> > > see that the device has a 32-bit DMA mask and either bounce or IOMMU-map > >> > > the memory so that it appears below 4GB. > >> > > >> > That's true. It would of course be more efficient for the buffer to be > >> > allocated below 4 GB, but it should work okay either way. Daniel, do > >> > you have any idea why it fails? > >> > >> No, and I can't do real tests as I lack a 64bit machine. I'll do some > >> more investigation later today, but for now the only explanation I have > >> is that not the remapped DMA buffer is used eventually by the EHCI code > >> but the physical address of the original buffer. > >> > >> It would of course be best to fix the whole problem at this level, if > >> possible. > > > > It definitely needs to be fixed at this level. But I still think it's > > appropriate to have new USB core functions for allocating and > > deallocating I/O memory. The additional price is small compared to > > constantly bouncing the buffers. > > > > Pedro, in the hope of tracking down the problem, can you apply this > > patch and see what output it produces in the system log when the > > "interference" happens? (Warning: It will produce quite a lot of > > output whenever you send data to the audio device -- between 500 and > > 1000 lines per second.) > Hi Alan, > > here is the output of the patch you sent me when the interference is triggered. > > The log is long, 1.3mb in size. I don't see anything suspicious. The transfer_buffer addresses repeat every 32 URBs, and the DMA addresses cycle almost entirely uniformly from 0x20000000 to 0x23ffffff in units of 0x2000 (there are a few gaps where the interval is a little bigger). Alan Stern _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
