Sigh. It looks like yet another aspect of USB power management is broken. If you plug in a USB 3.0 device into a USB 2.0 port on Intel Haswell-ULT systems, many devices fail to enumerate, or stop responding to SCSI commands. The end result is that many USB 3.0 devices simply don't work when plugged into USB 2.0 ports, on either Ubuntu or ChromeOS (or any distro that has the BESL support patches). Bus traces are here, if anyone is interested: https://plus.google.com/photos/116960357493251979546/albums/5927302519338721425 This issue also shows up under Windows, and their solution was to disable USB 2.0 Link PM for all devices, except for those that are on internal ports, or external devices that advertise BESL support instead of the older HIRD support in their USB 2.0 BOS descriptor. The first patch disables USB 2.0 Link PM by default, and only re-enables it when userspace writes 1 to /sys/bus/usb/devices/../power/usb2_hardware_lpm. Mathias is working on a further patch to enable USB 2.0 Link PM for internal devices or devices that have BESL support. Julius reported that the same devices that fail under the Intel Haswell-ULT host work fine under the Synopsys DesignWare3 xHCI host controller, when the unmerged patch to enable USB 2.0 Link PM for xhci-platform devices is applied: http://marc.info/?l=linux-kernel&m=137704093406359&w=2 My hypothesis is that the Synopsys host doesn't go into L1 if the device NAKs a transfer, only when the bus is idle. That way, it doesn't have to depend on L1 remote wakeup, which is broken for these devices. I don't have a way to confirm that though. Paul, is the Synopsys host working around these broken devices? I do want to allow the Synopsys host to have USB 2.0 Link PM enabled if the host has a way to work around these broken devices. Paul and Julius, let's work out a solution to do this on top of these patches. I suspect that the solution may be to add an update_device method to xhci-plat that sets udev->usb2_hw_lpm_allowed, calls xhci_update_device, and then calls usb_set_usb2_hardware_lpm(). We'll have to wait for the updated patches from Mathias though. Sarah Sharp -- 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
