> From: Sarah Sharp [mailto:sarah.a.sharp@xxxxxxxxxxxxxxx] > Sent: Tuesday, September 24, 2013 2:29 PM > > 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 ... > 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 Did Julius verify with a USB analyzer that the LPM transactions are actually happening when using our host? I wasn't able to access the USB traces you pointed to above to see if there's a trace there. > 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? Not that I know of. I don't think we have done much LPM testing with USB 3.0 devices connected at USB 2.0 speeds. Glad to hear it works with the Linux driver. -- Paul -- 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
