usb: Don't disable Latency tolerance Messaging (LTM) before port reset

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Thu, Mar 01, 2018 at 01:15:28PM +0200, Mathias Nyman wrote:
> Disabing Latency Tolerance Messaging before port reset is unnecessary.
> LTM is automatically disabled at port reset.
> 
> If host can't communicate with the device the LTM message will fail, and
> the hub driver will unnecessarily do a logical disconnect.
> Broken communication is ofter the reason for a reset in the first place.
> 
> Additionally we can't guarantee device is in a configured state,
> epecially in reset-resume case when root hub lost power.
> LTM can't be modified unless device is in a configured state.
> 
> Just remove LTM disabling before port reset.
> 
> Details about LTM and port reset in USB 3 specification:
> 
> USB 3 spec section 9.4.5
> "The LTM Enable field can be modified by the SetFeature() and
> ClearFeature() requests using the LTM_ENABLE feature selector.
> This field is reset to zero when the device is reset."
> 
> USB 3 spec section 9.4.1
> "The device shall process a Clear Feature (U1_Enable or U2_Enable or
> LTM_Enable) only if the device is in the configured state."
> 
> Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
> ---
>  drivers/usb/core/hub.c | 12 +++---------
>  1 file changed, 3 insertions(+), 9 deletions(-)

Is this causing problems now such that we should get this to older
kernels as well?

thanks,

greg k-h
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