Hi, On Thu, Jan 21, 2016 at 1:28 PM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > John, Doug, or anyone else: > > I've got a Raspberry Pi 2B and I'm trying to use it with a compound > device. The device has a High-Speed hub with a Full-Speed function > permanently attached to port 4. > > The RPi detects the function but fails to initialize it. My bus > analyzer shows the reason why: A Start Split packet sent to the > device's internal hub for delivery to the FS function contained these > bytes: > > 78 44 01 c0 > > 0x78 is the SPLIT packet ID. 0x44 is the hub's bus address, with a 0 > in the high-order bit to indicate a Start Split. 0x01 is supposed to > be the port number in the hub (with a 0 in the high-order bit to > indicate the target device is Full Speed). The final 0xc0 is the CRC > with a few extra uninteresting bits. > > The problem here is the third byte. It is set to 0x01 even though the > port number is 4. As a result, the packet never gets delivered and the > host controller is unable to communicate with the target function. > > (By contrast, when the same device was attached to a laptop PC instead > of the RPi, the bus analyzer showed the SPLIT packet contained 78 06 > 04 60, as one would expect.) > > Now oddly enough, when I ran a similar test on the RPi using a > Low-Speed target device, it worked perfectly. In this case the device > was attached to port 5 of the HS hub, and the third byte of the SPLIT > packet was 0x85 (high-order bit is on to indicate Low Speed). > > Is this a bug in the Pi's host controller hardware? Or a bug in the > dwc_otg driver? The kernel I tested was current Raspbian, 4.1.15-v7+. > > Is this a known problem? Is there any reasonable way to fix it? This doesn't sound familiar to me, but as far as I know all the official Raspberry Pi kernels use a pretty different dwc2 driver. See the (non-mainline) code in drivers/usb/host/dwc_otg/ in the Raspberry Pi tree at <https://github.com/raspberrypi/linux.git>. The Raspberry Pi driver and the mainline driver are pretty different (though they have the same heritage). As far as I remember the Raspberry Pi driver has feature to enable FIQ for helping deal with some of the dwc2 issues. That gives it a chunk of code that's totally rewritten... It would be really interesting to see if the patch series I just posted helps you (it fixes lots of problems in the mainline driver with splits), though it might still not be enough on the Raspberry Pi since the CPU clock there is much slower than on my 1.8GHz A12-based system and thus maybe FIQ is a must have there... Anyway, sorry if that's not terribly helpful. :( John may have more familiarity with the non-mainline driver (or know people who are more familiar with it). -Doug -- 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
