On Mon, 10 May 2010, David Woodhouse wrote: > On Mon, 2010-05-10 at 11:50 +0900, FUJITA Tomonori wrote: > > On Fri, 7 May 2010 10:51:10 -0400 (EDT) > > Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > > > > On Fri, 7 May 2010, Daniel Mack wrote: > > > > > > > > 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. > > > > > > At one point we tried an experiment, printing out the buffer and DMA > > > addresses. I don't recall seeing anything obviously wrong, but if an > > > IOMMU was in use then that might not mean anything. Is it possible > > > that the IOMMU mappings sometimes get messed up for addresses above 4 > > > GB? > > > > You mean that an IOMMU could allocate an address above 4GB wrongly? If > > so, IIRC, all the IOMMU implementations use dev->dma_mask and > > dev->coherent_dma_mask properly. And the DMA address space of the > > majority of IOMMUs are limited less than 4GB. > > The Intel IOMMU code will use dev->dma_mask and dev->coherent_dma_mask > properly. It is not limited to 4GiB, but it will tend to give virtual > DMA addresses below 4GiB even when a device is capable of more; it'll > only give out higher addresses when the address space below 4GiB is > exhausted. What I meant was: Is it possible that the IOMMU code will return a virtual DMA address before 4 GB but will somehow forget to actually map that address to the data buffer? The problem goes away when Pedro boots with mem=4G. And the dma_mask value is set properly (in fact, the ehci-hcd driver currently doesn't use 64-bit DMA at all). If anyone wants to see the debug log entries showing the buffer and DMA addresses, they are attached to this email message: http://marc.info/?l=linux-kernel&m=127076841801054&w=2 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? 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
