On Fri, Aug 10, 2012 at 3:38 AM, Sarah Sharp <sarah.a.sharp@xxxxxxxxxxxxxxx> wrote: > 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. > I will try to collect the log when I have the laptops handy. >> 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. > Frankly, IMHO, I think the patch is not about to trust or not to trust the BIOS. I think this patch just does what the registers are designed to do. What if there is a good BIOS claiming some ports not to be switchable but kernel does so. Isn't it a bad kernel too? :-) cheers, -kengyu -- 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
