Messages in this thread | | | From | Bjørn Mork <> | Subject | Re: [PATCH v2] USB: serial: qcserial: Support for SDX55 based Sierra Wireless 5G modules | Date | Fri, 02 Jul 2021 09:32:28 +0200 |
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Stefan Brüns <stefan.bruens@rwth-aachen.de> writes:
> On Donnerstag, 24. Juni 2021 13:15:07 CEST Bjørn Mork wrote: >> Johan Hovold <johan@kernel.org> writes: >> > Could you please also post the output of usb-devices (or lsusb -v) for >> > this device in MBIM mode? >> >> Yes, this would be nice to have. > > See below. > >> I suspect that this device is like other SDX55 devices we've seen, using >> class/subclass/function to map the vendor specific functions >> too. Dropping static interface numbers. If correct, then the patch is >> bogus and the interface numbers might change based on firmware version >> and configuration. > > Do you really expect Sierra do to something sensible? According to their > documentation functions are matched by interface numbers.
Well... I expect them to be as sensible as any other vendor. And I expect docs to be intendend as guidance only ;-)
> They still use broken interface descriptors with holes in interface numbering > (i.e. interface number 2 does not exist, which violates the USB standard).
Right. Wrt the violation, I think that train left a decade ago.
> Interface Descriptor: > bLength 9 > bDescriptorType 4 > bInterfaceNumber 3 > bAlternateSetting 0 > bNumEndpoints 3 > bInterfaceClass 255 Vendor Specific Class > bInterfaceSubClass 0 > bInterfaceProtocol 0 [..] > Interface Descriptor: > bLength 9 > bDescriptorType 4 > bInterfaceNumber 4 > bAlternateSetting 0 > bNumEndpoints 2 > bInterfaceClass 255 Vendor Specific Class > bInterfaceSubClass 255 Vendor Specific Subclass > bInterfaceProtocol 48
So Sierra do follow the same pattern we've seen on other X55 devices:
ff/00/00 - AT ff/ff/30 - QCDM
See commits
accf227de4d2 ("USB: serial: option: Add support for Quectel RM500Q") d6c1ddd938d8 ("USB: serial: option: add Quectel EM160R-GL")
for other examples.
This obviously doesn't make any difference if your configuration is the only one. But I believe that is unlikely. There are probably ways the layout can be changed, even if currenly not documented. The advantage of class/subclass/protocol matching to function is that it works regardless of the number of functions and their interface number.
Bjørn
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