FCC authentication with QMI over MBIM; try 1 -- Logs

Bjørn Mork bjorn at mork.no
Mon Jul 11 08:49:17 UTC 2016

Aleksander Morgado <aleksander at aleksander.es> writes:
> On Fri, Jul 8, 2016 at 11:17 PM, Bjørn Mork <bjorn at mork.no> wrote:
>> Do you all have the same weird looking BOS on your EM7455s?
> My EM7455 here does say SuperSpeed:
> Binary Object Store Descriptor:
>   bLength                 5
>   bDescriptorType        15
>   wTotalLength           22
>   bNumDeviceCaps          2
>   USB 2.0 Extension Device Capability:
>     bLength                 7
>     bDescriptorType        16
>     bDevCapabilityType      2
>     bmAttributes   0x00000000
>       (Missing must-be-set LPM bit!)
>   SuperSpeed USB Device Capability:
>     bLength                10
>     bDescriptorType        16
>     bDevCapabilityType      3
>     bmAttributes         0x00
>     wSpeedsSupported   0x000f
>       Device can operate at Low Speed (1Mbps)
>       Device can operate at Full Speed (12Mbps)
>       Device can operate at High Speed (480Mbps)
>       Device can operate at SuperSpeed (5Gbps)
>     bFunctionalitySupport   1
>       Lowest fully-functional device speed is Full Speed (12Mbps)
>     bU1DevExitLat           1 micro seconds
>     bU2DevExitLat         500 micro seconds

Interesting.  And I see that it also has the missing LPM bit, so that's
obviously a red herring.

Does this mean that you also can use it as an SS device?  I did some
mailing list digging and found that  every single person posting an lsusb
output from a Lenovo laptop has had the EM7455 connected as a HS device.
That is, I'm sort of guessing for most of them, since they don't have "-v".
But there is only one xhci controller, so the bus number is an easy way
to figure out SS or HS:

bjorn at miraculix:~$ lsusb
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 005: ID 138a:0090 Validity Sensors, Inc. 
Bus 001 Device 004: ID 04f2:b531 Chicony Electronics Co., Ltd 
Bus 001 Device 003: ID 8087:0a2b Intel Corp. 
Bus 001 Device 016: ID 1199:9079 Sierra Wireless, Inc. 
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

I'm pretty sure bus #1 will always be HS. I haven't actually looked at
the xhci driver, but I assume it registers the buses in a fixed order.
And everyone single log and lsusb from a Lenovo with an EM7455 shows the
modem as "1-2".  I.e. on port #2 (fixed for the wwan m.2 slot) and bus #1.

But I do wonder if I understand the connection issues involved.  Is it
so that Lenovo didn't wire up USB3 to the wwan m.2 slot, and the EM7455
firmware adapts to that by hiding the SS capability?  The actual speed
selection should be a controller thing, shouldn't it?  Or is the kernel
taking any part of the decision?  I guess I have to read up on this
stuff.  USB3 is pretty new to me :)


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