Re: [TESTPATCH v2] xhci: fix usb2 resume timing and races.

[Mathias Nyman]

On 05.12.2015 06:02, Daniel J Blueman wrote:
> On 1 December 2015 at 16:26, Mathias Nyman
> <mathias.nyman@xxxxxxxxxxxxxxx> wrote:
> > usb2 ports need to signal resume for 20ms before moving to U0 state.
> > Both device and host can initiate resume.
> >
> > On host initated resume port is set to resume state, sleep 20ms,
> > and finally set port to U0 state.
> >
> > On device initated resume a port status interrupt with a port in resume
> > state in issued. The interrupt handler tags a resume_done[port]
> > timestamp with current time + 20ms, and kick roothub timer.
> > Root hub timer requests for port status, finds the port in resume state,
> > checks if resume_done[port] timestamp passed, and set port to U0 state.
> >
> > There are a few issues with this approach,
> > 1. A host initated resume will also generate a resume event, the event
> >     handler will find the port in resume state, believe it's a device
> >     initated and act accordingly.
> >
> > 2. A port status request might cut the 20ms resume signalling short if a
> >     get_port_status request is handled during the 20ms host resume.
> >     The port will be found in resume state. The timestamp is not set leading
> >     to time_after_eq(jiffoes, timestamp) returning true, as timestamp = 0.
> >     get_port_status will proceed with moving the port to U0.
> >
> > 3. If an error, or anything else happends to the port during device
> >     initated 20ms resume signalling it will leave all device resume
> >     parameters hanging uncleared preventing further resume.
> >
> > Fix this by using the existing resuming_ports bitfield to indicate if
> > resume signalling timing is taken care of.
> > Also check if the resume_done[port] is set  before using it in time
> > comparison. Also clear out any resume signalling related variables if port
> > is not in U0 or Resume state.
> >
> > v2. fix parentheses when checking for uncleared resume variables.
> > we want: if ((unclear1 OR unclear2 ) AND !in_resume AND !in_U3) { .. }
> >
> > Signed-off-by: Mathias Nyman <mathias.nyman@xxxxxxxxxxxxxxx>
>
> Excellent; this correctly prevents the cyclic chain of suspend
> attempts, resolving the issue.
>
> Tested-by: Daniel J Blueman <daniel@xxxxxxxxx>
>
> Thanks Mathias!
>    Daniel

Thanks for testing it
I'll do some minor cleanups and add it to the queue

-Mathias
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