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Message-ID: <20140521002720.GC997@kroah.com> Date: Wed, 21 May 2014 09:27:20 +0900 From: Greg KH <gregkh@...uxfoundation.org> To: Dan Williams <dan.j.williams@...el.com> Cc: Takashi Iwai <tiwai@...e.de>, Mathias Nyman <mathias.nyman@...ux.intel.com>, USB list <linux-usb@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Sarah Sharp <sarah.a.sharp@...ux.intel.com>, Holger Hans Peter Freyther <holger@...ji-mobile.com>, Oliver Neukum <oneukum@...e.de> Subject: Re: [PATCH 02/10] xhci: 'noxhci_port_switch' kernel parameter On Tue, May 20, 2014 at 03:40:16PM -0700, Dan Williams wrote: > On Tue, May 20, 2014 at 1:34 PM, Greg KH <gregkh@...uxfoundation.org> wrote: > > On Tue, May 20, 2014 at 11:25:37AM -0700, Dan Williams wrote: > >> On Tue, May 20, 2014 at 2:51 AM, Takashi Iwai <tiwai@...e.de> wrote: > >> > At Tue, 20 May 2014 12:47:36 +0300, > >> > Mathias Nyman wrote: > >> >> > >> >> On 05/20/2014 04:01 AM, Greg KH wrote: > >> >> > On Thu, May 08, 2014 at 07:25:55PM +0300, Mathias Nyman wrote: > >> >> >> From: Dan Williams <dan.j.williams@...el.com> > >> >> >> > >> >> >> Add a command line switch for disabling ehci port switchover. Useful > >> >> >> for working around / debugging xhci incompatibilities where ehci > >> >> >> operation is available. > >> >> >> > >> >> >> Reference: http://marc.info/?l=linux-usb&m=138920063001509&w=2 > >> >> >> > >> >> >> Cc: Sarah Sharp <sarah.a.sharp@...ux.intel.com> > >> >> >> Cc: Mathias Nyman <mathias.nyman@...ux.intel.com> > >> >> >> Cc: Holger Hans Peter Freyther <holger@...ji-mobile.com> > >> >> >> Suggested-by: Alan Stern <stern@...land.harvard.edu> > >> >> >> Signed-off-by: Dan Williams <dan.j.williams@...el.com> > >> >> >> Signed-off-by: Mathias Nyman <mathias.nyman@...ux.intel.com> > >> >> >> --- > >> >> >> Documentation/kernel-parameters.txt | 3 +++ > >> >> >> drivers/usb/host/pci-quirks.c | 15 +++++++++++++-- > >> >> >> 2 files changed, 16 insertions(+), 2 deletions(-) > >> >> >> > >> >> >> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt > >> >> >> index 4384217..fc3403114 100644 > >> >> >> --- a/Documentation/kernel-parameters.txt > >> >> >> +++ b/Documentation/kernel-parameters.txt > >> >> >> @@ -2251,6 +2251,9 @@ bytes respectively. Such letter suffixes can also be entirely omitted. > >> >> >> > >> >> >> nox2apic [X86-64,APIC] Do not enable x2APIC mode. > >> >> >> > >> >> >> + noxhci_port_switch > >> >> >> + [USB] Use EHCI instead of XHCI where available > >> >> >> + > >> >> > > >> >> > Ugh, I really don't like new command line options. > >> >> > > >> >> > Especially one that isn't very well documented. Why would someone want > >> >> > to enable this? What problem is it solving? Can we detect this > >> >> > automatically and do it for the user? Is this just for prototype > >> >> > hardware that has not shipped? What hardware needs this? > >> >> > > >> >> > I need a whole lot more documentation at the very least before I will > >> >> > apply this. > >> >> > > >> >> > >> >> On Intel hardware with both ehci and xhci controllers we can select if a usb2 port > >> >> is controlled by ehci or xhci. This capability can be checked from Intel xhci pci > >> >> config space. Xhci driver checks this on boot and switches over the supported ports. > >> >> > >> >> This is a feature in Intel Panther point and later chipsets, in shipped hardware. > >> >> Its working quite well in most cases, but sometimes vendors claim they support > >> >> switchover, but then forget to connect some wires, and the usb2 port ends up dead > >> >> after switching. > >> >> > >> >> A recently found case is the Sony VAIO T-series. (I'll send you a different patch > >> >> for that shortly) > >> >> http://marc.info/?l=linux-usb&m=139993106029340&w=2 > >> >> > >> >> This is the extreme case that the usb2 ports appears completely dead. > >> >> Other reasons are that some devices might work better under ehci than xhci, > >> >> and users want to enforce the ehci opton. For powermanagement developers it's nice > >> >> to disable switchover as it turns out some hardware are quirky with port > >> >> switchover and suspend/resume. (might need to turn port back to ehci before > >> >> suspending). > >> >> > >> >> I don't think we can detect this automatically. > >> >> > >> >> Dan, can you add more documentation to this patch? > >> > > >> > While we're at it: can we implement a bitmask instead? > >> > > >> > We've seen lots of HP laptops having Webcams or BT devices that don't > >> > work XHCI but only with EHCI. For making them working properly, the > >> > specific xhci ports have to be disabled. But, we don't want to kill > >> > the whole XHCI at all. The single boolean option doesn't work for > >> > such a case. > >> > > >> > >> I'm not sure we want to make this more complex. Ideally this is just > >> a stop-gap measure for users to workaround incompatibilities in xhci > >> while the xhci fix is identified. > > > > We can't use a kernel command line option as a "stop-gap", sorry. Let's > > just fix the real problem here. > > > > Greg, > > Sorry, I don't think it is fair to users to force them to re-compile > their kernel to get their device to work. I totally agree. > Granted, I'm new to USB > development, but the rate of reports of endpoint devices that mess up > and require quirks in the hcd-driver or usb-core seems un-ending to > me. So, I don't think it is fair to expect that the tide of quirky > devices will be stemmed in any reasonable amount of time. Having a > "works with noxhci_port_switch" report from users is good data (hmm, I > think a printk to tell users to file a report upstream if the option > resolves their issue is needed). How about just adding a debugfs file instead? That way, once you fix this, we can then remove it and no one will care. thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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