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.) > > Alan Stern > > > > Index: 2.6.33/drivers/usb/core/hcd.c > =================================================================== > --- 2.6.33.orig/drivers/usb/core/hcd.c > +++ 2.6.33/drivers/usb/core/hcd.c > @@ -1395,6 +1395,10 @@ int usb_hcd_submit_urb (struct urb *urb, > usbmon_urb_submit_error(&hcd->self, urb, status); > goto error; > } > + if (usb_endpoint_is_isoc_out(&urb->ep->desc)) > + dev_info(&urb->dev->dev, "Iso xfer %p dma %llx\n", > + urb->transfer_buffer, > + (unsigned long long) urb->transfer_dma); > > if (is_root_hub(urb->dev)) > status = rh_urb_enqueue(hcd, urb); > > I'll do it tonight and send you the results tomorrow morning. Do you want CONFIG_USB_DEBUG enabled or disabled? Pedro -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
