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SubjectRe: [PATCH][RFC] usbhid: enable autosuspend for internal devices
On Fri, 26 Jun 2015, Greg Kroah-Hartman wrote:

> > This doesn't do what the patch title says. USB_DEVICE_FIXED means that
> > the device can't be unplugged from its upstream port. It doesn't mean
> > the device is internal to the computer.
> >
> > As an example, consider a composite Apple keyboard, which has an
> > internal 3-port USB hub where two of the hub's ports are exposed on the
> > edge of the keyboard case and the keyboard controller is permanently
> > attached to the third hub port. Then the controller device would be
> > marked USB_DEVICE_FIXED, even though the whole thing is external to
> > the computer and can be unplugged.
> >
>
> Is that really how those devices are marked? I can't find any of my
> keyboard with hubs that mark things that way.

My Apple keyboard isn't here at the moment, and I don't remember
exactly what its hub descriptor contains. In theory, it _should_ mark
the permanently attached port as non-removable.

I can test it next week, if you would like to see the actual values.

> > Also, are you really certain this is safe? Aren't there a number of
> > built-in keyboards that will work badly if you allow them to
> > autosuspend?
>
> udev has been doing this for a while now by default, with no reports of
> problems, so I think we should be safe.

I thought udev used a whitelist of devices known to work okay with
autosuspend. Does it really turn on autosuspend for _every_ USB HID
device that is marked as removable?

(Come to think of it, given the bug in the hub driver, no device
attached directly to the root hub will _ever_ be marked as removable
AFAICS. So maybe that bug is masking possible regressions.)

Alan Stern



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