linux-kernel - Re: [PATCH] Intel xhci: Only switch the switchable ports

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Message-ID: <20120809193859.GD14429@xanatos>
Date:	Thu, 9 Aug 2012 12:38:59 -0700
From:	Sarah Sharp <sarah.a.sharp@...ux.intel.com>
To:	Keng-Yu Lin <kengyu@...onical.com>
Cc:	Greg Kroah-Hartman <gregkh@...e.de>, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Intel xhci: Only switch the switchable ports

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@...ux.intel.com> 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
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