Re: [3.16.1 BISECTED REGRESSION]: Simtec Entropy Key (cdc-acm) broken in 3.16

[Johan Hovold <johan@kernel.org>]

[ +CC: linux-usb ]

On Wed, Oct 22, 2014 at 04:36:59PM +0100, Nix wrote:
> On 22 Oct 2014, Johan Hovold outgrape:
> 
> > On Wed, Oct 22, 2014 at 10:31:17AM +0100, Nix wrote:
> >> On 14 Oct 2014, Johan Hovold verbalised:
> >> 
> >> > On Sun, Oct 12, 2014 at 10:36:30PM +0100, Nix wrote:
> >> >> I have checked: this code is being executed against a symlink that
> >> >> points to /dev/ttyACM0, and the tcsetattr() succeeds. (At least, it's
> >> >> succeeding on the kernel I'm running now, but of course that's 3.16.5
> >> >> with this commit reverted...)
> >> >
> >> > You could verify that by enabling debugging in the cdc-acm driver and
> >> > making sure that the corresponding control messages are indeed sent on
> >> > close.
> >> 
> >> I have a debugging dump at
> >> <http://www.esperi.org.uk/~nix/temporary/cdc-acm.log>; it's fairly
> >
> > What kernel were you using here? The log seems to suggest that it was
> > generated with the commit in question reverted.
> 
> Look now :) (the previous log is still there in cdc-acm-reverted.log.)

Unfortunately, it seems the logs are incomplete. There are lots of
entries missing (e.g. "acm_tty_install" when opening, but also some
"acm_submit_read_urb"), some of which were there in your first log.

Also you can disable the "acm_tty_write - count" output, which isn't
really useful here.

> This contains two boots -- one on which the USB key worked, and the next
> (with an identical kernel) with which the key was broken. (I'm not sure
> whether this problem happens at startup or shutdown time, so it seemed
> best to provide both.)

That's a good idea.

Is it only after reboot you've seen the device fail? What if you
physically disconnect and reconnect the device instead, or simply
repeatedly open and close it?

Johan