ThinkPad X1 Yoga: LTE Sierra EM7455 on Linux Ubuntu 16.04

[Hacker-CB]

Hello!

I have bought ThinkPad X1 Yoga and installed Ubuntu 16.04. All works, except LTE modem (Sierra EM7455).

So, when all patches for support this modek will be released to the Linux Kernel?

[x220forme]

Hello

I'm not a Linux user nor expert anything Linux related.

But, let me inform you Linux kernel starting at 3.8+ comes with new "CDC MBIM" driver. MBIM capabilities are enough to support modern LTE modems w/out manufacturer's drivers.

So, google a bit, I hope you'll find a solution.

UPD

FYI: https://www.kernel.org/doc/Documentation/networking/cdc_mbim.txt

[bmork]

The final part of the EM7455 Linux driver support is going in Linux v4.7 which will be released in a couple of weeks.  It will also be backported to the currently maintained stable kernels, so you should eventually get it through Ubuntu kernel updates.

Sorry it took this long. In theory, any MBIM modem should just work with the existing Linux drivers.  But it turned out that the EM7455 needed a small delay during initialization, or it would silently fail to work.  The "fix" is a single line of code:

https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/drivers/net/usb/cdc_ncm.c?id=...

But believe me:  It took quite a lot of experimenting and failing to figure this out...

In addition to that driver fix, you will also need the absolutely latest version (v1.6) of ModemManager, which also requires recent versions of libqmi (v1.16) and libmbim (v1.14).  The reason for this is that the Lenovo version of the EM7455 is configured with a feature we know as "FCC Auth".  It is designed to keep the radio off until the OS has told the modem it is OK to enable it. In Linux, the support for doing this automatically was added in ModemManager v1.6. Which isn't quite ready yet.  It is currently at v1.6-rc4 (also known as v1.5.993).

These newest versions of ModemManager, libqmi and libmbim are available in Debian sid (unstable) now.  This usually means that they are also availble in Ubuntu, but you might have to wait for the next release before they are default.

I can testify that it works.  I am happily using an X1 Carbon in Debian sid, with a fully functional EM7455.  I am not using a Debian kernel at the moment though, but a self-built v4.7-rc7.  This should not be necessary in a couple of weeks, as I expect Debian sid will move to 4.7 as soon as it is released.

Bjørn (one of the two cdc_mbim authors)

[x220forme]

Bjørn,

what maximum data speed did you achieve using x1c and em7455? Did the network mode LTE-A work actually during the tests?

Based on your another thread:
https://forums.lenovo.com/t5/ThinkPad-X-Series-Laptops/x1-carbon-4th-gen-no-USB3-superspeed-for-wwan...

[bmork]

---

x220forme wrote:
Bjørn,

what maximum data speed did you achieve using x1c and em7455? Did the network mode LTE-A work actually during the tests? What can you say about USB 3.0 support in the x1c m.2 slot with em7455 installed?

Have a look at this thread:
https://forums.lenovo.com/t5/ThinkPad-X-Series-Laptops/x1-carbon-4th-gen-no-USB3-superspeed-for-wwan...

---

That thread was also me :-)

But, yes, I can answer the LTE-A question:  It's well hidden in the Qualcomm firmware, but I do see LTE-A being enabled when I do speed tests. Of course, that doesn't work right now when I was going to collect an example output to post here...  In any case, the network supports bundling of 20 MHz channels on B3 and B7 and a 10 MHz channel on B20

[x220forme]

Sure, I seen and read, that link is more for the forummers )

10+20 MHz, in theory, allow to achieve the speed about to 220 Mbps. You tested and mentioned 130 Mbps. Such difference is very significant if it's caused by the USB interface.

At the end of July I hope to get em7455 and use it in the x220 and, later, test in the x1c gen3. But unfortunately I don't watch cellular networks with LTE-A support in my area. So, there will be tests regarding USB support only.

[bmork]

---

x220forme wrote:
Sure, I seen and read, that link is more for the forummers )

10+20 MHz, in theory, allow to achieve the speed about to 220 Mbps. You tested and mentioned 130 Mbps. Such difference is very significant if it's caused by the USB interface.

---

The network can do 10+20, but it can also do 20+20 (and actually more, but that's the limit of the EM7455).  I got it working now.  Carrier aggregation (CA) is deactivated before starting download:

root@miraculix:/tmp# qmicli -p -d /dev/cdc-wdm0 --device-open-mbim   --nas-get-lte-cphy-ca-info
[/dev/cdc-wdm0] Successfully got carrier aggregation info
DL Bandwidth: '20'
Secondary Cell Info
        Physical Cell ID: '65'
        TX Channel: '1450'
        DL Bandwidth: '20'
        LTE Band: 'eutran-3'
        State: 'deactivated'
Primary Cell Info
        Physical Cell ID: '235'
        TX Channel: '3050'
        DL Bandwidth: '20'
        LTE Band: 'eutran-7'
Secondary Cell index: '1'

Then after downloading for a while, CA is automatically activated:

root@miraculix:/tmp# qmicli -p -d /dev/cdc-wdm0 --device-open-mbim   --nas-get-lte-cphy-ca-info
[/dev/cdc-wdm0] Successfully got carrier aggregation info
DL Bandwidth: '20'
Secondary Cell Info
        Physical Cell ID: '65'
        TX Channel: '1450'
        DL Bandwidth: '20'
        LTE Band: 'eutran-3'
        State: 'activated'
Primary Cell Info
        Physical Cell ID: '235'
        TX Channel: '3050'
        DL Bandwidth: '20'
        LTE Band: 'eutran-7'
Secondary Cell index: '1'

Don't worry about the "TX channel". That's a typo.  It is RX.

[x220forme]

And the DL speed, in case CA 10+20 and 20+20? )

[bmork]

---

x220forme wrote:
And the DL speed, in case CA 10+20 and 20+20? )

---

It varies of course, depending on both the signal and other users. But the absolute max seems to be 130 Mbits/s.  I don't actually know what the limiting factor is.  Which is why I had high hopes of finally testing with USB3 to eliminate that variable.

[djao]

If you don't want to wait, you can use the EM7455 modem in Ubuntu 16.04 right now, by upgrading to the respective versions of libqmi (1.16.0), libmbim (1.14.0), and modemmanager (1.6.0) from Yakkety Yak. There is no need to patch the kernel as long as you're on the latest 16.04 kernel, as the latest kernel already includes the necessary kernel patch.