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

Oliver Neukum [off-list ref] writes:

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

quoted

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.

Could be, but I don't think so.  The above code is effectively a noop
unless the function is a combined NCM/MBIM function.  Something I've
never seen on a Sierra Wireless device (ignoring the infamous EM7345,
which really is an Intel device).

This is a typical example of a Sierra Wireless modem configured for
MBIM:

P:  Vendor=1199 ProdID=9079 Rev= 0.06
S:  Manufacturer=Sierra Wireless, Incorporated
S:  Product=Sierra Wireless EM7455 Qualcomm Snapdragon X7 LTE-A
S:  SerialNumber=LF615126xxxxxxx
C:* #Ifs= 2 Cfg#= 1 Atr=a0 MxPwr=500mA
A:  FirstIf#=12 IfCount= 2 Cls=02(comm.) Sub=0e Prot=00
I:* If#=12 Alt= 0 #EPs= 1 Cls=02(comm.) Sub=0e Prot=00 Driver=(none)
E:  Ad=82(I) Atr=03(Int.) MxPS=  64 Ivl=32ms
I:* If#=13 Alt= 0 #EPs= 0 Cls=0a(data ) Sub=00 Prot=02 Driver=(none)
I:  If#=13 Alt= 1 #EPs= 2 Cls=0a(data ) Sub=00 Prot=02 Driver=(none)
E:  Ad=81(I) Atr=02(Bulk) MxPS= 512 Ivl=0ms
E:  Ad=01(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms


The control interface of plain MBIM functions will always have a single
altsetting, like the example above. So cdc_ncm_select_altsetting(intf)
returns "0", while CDC_NCM_COMM_ALTSETTING_MBIM is "1".


Just for reference, using the Intel^H^H^H^H^HEM7345 as example, this is
what a combined NCM/MBIM function looks like:


P:  Vendor=1199 ProdID=a001 Rev=17.29
S:  Manufacturer=Sierra Wireless Inc.
S:  Product=Sierra Wireless EM7345 4G LTE
S:  SerialNumber=013937000xxxxxx
C:* #Ifs= 4 Cfg#= 1 Atr=e0 MxPwr=100mA
A:  FirstIf#= 0 IfCount= 2 Cls=02(comm.) Sub=0d Prot=00
A:  FirstIf#= 2 IfCount= 2 Cls=02(comm.) Sub=02 Prot=01
I:  If#= 0 Alt= 0 #EPs= 1 Cls=02(comm.) Sub=0d Prot=00 Driver=cdc_mbim
E:  Ad=81(I) Atr=03(Int.) MxPS=  64 Ivl=1ms
I:* If#= 0 Alt= 1 #EPs= 1 Cls=02(comm.) Sub=0e Prot=00 Driver=cdc_mbim
E:  Ad=81(I) Atr=03(Int.) MxPS=  64 Ivl=1ms
I:  If#= 1 Alt= 0 #EPs= 0 Cls=0a(data ) Sub=00 Prot=01 Driver=cdc_mbim
I:  If#= 1 Alt= 1 #EPs= 2 Cls=0a(data ) Sub=00 Prot=01 Driver=cdc_mbim
E:  Ad=82(I) Atr=02(Bulk) MxPS= 512 Ivl=0ms
E:  Ad=02(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms
I:* If#= 1 Alt= 2 #EPs= 2 Cls=0a(data ) Sub=00 Prot=02 Driver=cdc_mbim
E:  Ad=82(I) Atr=02(Bulk) MxPS= 512 Ivl=0ms
E:  Ad=02(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms
I:* If#= 2 Alt= 0 #EPs= 1 Cls=02(comm.) Sub=02 Prot=01 Driver=(none)
E:  Ad=83(I) Atr=03(Int.) MxPS=  64 Ivl=1ms
I:* If#= 3 Alt= 0 #EPs= 2 Cls=0a(data ) Sub=00 Prot=00 Driver=(none)
E:  Ad=84(I) Atr=02(Bulk) MxPS= 512 Ivl=0ms
E:  Ad=04(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms


And this is what the code you quote is trying to deal with.  Note the
different subclass of altsetting 0 and 1.... This is incredibly ugly.

FWIW, the modem in question cannot be an EM7345. That modem does not
have the static interface numbering oddity.  Another sign that it isn't
a true Sierra device.




Bjørn