On Fri, Aug 10, 2012 at 12:13:19AM +0800, Keng-Yu Lin wrote: > On Thu, Aug 9, 2012 at 10:24 PM, Sarah Sharp > <sarah.a.sharp@xxxxxxxxxxxxxxx> wrote: > > On Thu, Aug 09, 2012 at 05:31:51PM +0800, Keng-Yu Lin wrote: > >> With a previous patch to enable the EHCI/XHCI port switching, it switches > >> all the available ports. > >> > >> The assumption is not correct because the BIOS may expect some ports > >> not switchable by the OS. > > > > Why would the BIOS expect some ports to not be switchable? I know that > > we internally at Intel had discussed some theoretical reasons why it > > might not be good to switch some ports, but when I presented the > > original patch with this same code in it to Linux USB mailing list, both > > Alan and Greg said, "Why not unconditionally switch ports?" I had no > > good examples at the time. > > > > Is this causing issues with some particular BIOS? > > > > Yes, this is causing the internal webcam missing on the USB bus as I > observed on some HM70-based laptops. Does anything show up in dmesg when you turn on CONFIG_USB_XHCI_HCD_DEBUGGING? It would be good to know if it is totally not electrically present, or if there's some sort of xHCI hardware or software issue that's preventing the webcam from being enumerated. > The internal webcam is attached to one port that is controlled by the > xhci host. > But the other ports with the outer plugs work well after booting. I > cannot test the USB port of the internal webcam easily (without > tearing down the laptop :-/). > > I also tried some similar HM77-based models. HM77 has no this issue. > This could be some chipset mystery I am not aware now. Could be. Can you use any SMBIOS information to change the port switchover only for those HM70-based laptops? And is it a particular laptop vendor or all HM70 laptops? As Alan said, I would rather not trust the BIOS to provide the correct port mask. 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
