On Fri, 17 Jan 2014, Sarah Sharp wrote:
> > Allow me to propose an alternative.
> >
> > Let's do our best to treat root hubs the same as external hubs. This
> > means that udev->lpm_capable should be set the same way in
> > hub_port_init() and register_root_hub(): by calling
> > usb_device_supports_lpm(), which gets the information from the BOS
> > extended capabilities.
> >
> > In particular, xhci-hcd shouldn't go messing around with the innards of
> > the root hub structure. Instead of setting lpm_capable when it knows
> > how to calculate the timeout values, it should pass the necessary
> > information through the ss_cap descriptor, just like an external hub
> > would. Either don't provide that descriptor at all if you don't know
> > the timeout values, or else set those fields in the descriptor to
> > something invalid (and make usb_device_supports_lpm() test for it).
> >
> > And while we're at it, let's change the comment in
> > usb_device_supports_lpm() that says "All USB 3.0 must support LPM".
> > Not only is it ungrammatical, but as you point out, it is wrong for
> > some root hubs.
>
> I agree your alternative is much cleaner, and I agree we should try to
> treat roothubs like external hubs. I've made a patch (to be sent
> shortly) that fixes this.
>
> However, I would like to see the original bad commit ("usbcore: set
> lpm_capable field for LPM capable root hubs") reverted from the stable
> kernels, since it's been backported to 3.10, 3.11, and 3.12. I would
> rather go for the simple revert, since that's less likely to cause
> issues than new code.
Reverting Ksenia's patch from the stable kernels is okay with me.
Strictly speaking, I guess this means you have to revert it from the
current kernel as well, and then write your new patch to go on top of
the reversion.
Alan Stern
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