Re: [PATCH] usbnet: prevent device rpm suspend in usbnet_probe function

On Tue, 2016-11-08 at 13:44 -0500, Alan Stern wrote:

These problems could very well be caused by running at SuperSpeed
(USB-3) instead of high speed (USB-2).

Is there any way to test what happens when the device is attached to 
the computer by a USB-2 cable?  That would prevent it from operating at 
SuperSpeed.

The main point, however, is that the proposed patch doesn't seem to
address the true problem, which is that the device gets suspended
between probes.  The patch only tries to prevent it from being
suspended during a probe -- which is already prevented by the USB core.

But why doesn't it fail during normal operation?

I suspect that its firmware requires the altsetting

        /* should we change control altsetting on a NCM/MBIM function? */
        if (cdc_ncm_select_altsetting(intf) == CDC_NCM_COMM_ALTSETTING_MBIM) {
                data_altsetting = CDC_NCM_DATA_ALTSETTING_MBIM;
                ret = cdc_mbim_set_ctrlalt(dev, intf, CDC_NCM_COMM_ALTSETTING_MBIM);

to be set before it accepts a suspension.

	Regards
		Oliver