At Tue, 20 May 2014 11:25:37 -0700, Dan Williams wrote: > > On Tue, May 20, 2014 at 2:51 AM, Takashi Iwai <tiwai@xxxxxxx> 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@xxxxxxxxx> > >> >> > >> >> 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@xxxxxxxxxxxxxxx> > >> >> Cc: Mathias Nyman <mathias.nyman@xxxxxxxxxxxxxxx> > >> >> Cc: Holger Hans Peter Freyther <holger@xxxxxxxxxxxxxxxx> > >> >> Suggested-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> > >> >> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx> > >> >> Signed-off-by: Mathias Nyman <mathias.nyman@xxxxxxxxxxxxxxx> > >> >> --- > >> >> 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. The fact that it is a coarse hammer > at least, in my mind, keeps more pressure on identifying the necessary > xhci quirk/fix to make it as functional as ehci. We need that fix > anyways for platforms with xhci ports without an ehci companion, so > what purpose is served by letting users avoid xhci with finer > granularity? There are cases where only certain ports suffer from the problem of XHCI. The finer granularity allows user to identify the affected ports, and at least, more-or-less working state. But the main purpose of this option is to give the pressure to XHCI developers, then I agree with it. But, in that case, it must be documented properly. Namely, this option is only for testing/debugging, and shouldn't be applied to any running system for real use as a workaround. Takashi -- 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
