On Wed, 7 Apr 2010, Robert Hancock wrote: > >> The problem is appearantly the way the transfer buffer is allocated in > >> the drivers. In the snd-usb-caiaq driver, I used kzalloc() to get memory > >> which works fine on 32bit systems. On x86_64, however, it seems that > >> kzalloc() hands out memory beyond the 32bit addressable boundary, which > >> the DMA controller of the 32bit PCI-connected EHCI controller is unable > >> to write to or read from. Am I correct on this conclusion? > > > > That seems like the right answer. You are correct that an EHCI > > controller capable only of 32-bit memory accesses would not be able to > > use a buffer above the 4 GB line. > 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? Alan Stern -- 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
