Oliver Neukum <oneukum@xxxxxxxx> writes: > 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. 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 -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html