On Tue, 11 May 2010, Konrad Rzeszutek Wilk 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)' I don't know. We didn't print out the value of virt_to_phys(urb->transfer_buffer). All I can say is that urb->transfer_dma is the value returned by dma_map_single(). > (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? There are no calls to any dma_sync_* routines. Daniel will have to check me on this, but I believe that urb->transfer_buffer is filled before dma_map_single() is called and it isn't touched again until after dma_unmap_single() (which occurs before urb's completion handler is called). 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
