Dispatches from the X1 front

The first-gen Thinkpad X1: possibly the best laptop I've ever owned. Lasted three years, compared to the usual 12-18 months. It still runs, but the battery is down to about 40 minutes, and the (second!) keyboard is starting to lose keys.

The third-gen Thinkpad X1 Carbon: a little annoying at first: no SD slot, no h/w kill switch for the wireless, no spill-through keyboard (wtf guys, that was brilliant!). About 6 months in, the video glitches started: there is a short which corrupts video memory while using wifi. The fix, of course, is a replacement system board, which is great if you have a spare third-gen X1 Thinkpad Carbon lying around and can just up and change workstations like it's no big. Workaround: rfkill block wifi, or just get used to the strobe effect.

The latest: Thinkpad X1 Yoga. And let's just put it out there: this doesn't work out of the box like the previous two did. Lenovo and Intel seem to have backed off of their Linux commitment, though that's probably half their users these days (errybody else on the mobile, right?)

Here's the rundown on getting the X1 Yoga up and running with a Linux install.


Basic Linux

Debian 8.3.0 AMD64 netinst ISO if you were wise enough to buy the OneLink+ RJ45 ethernet adapter; otherwise, use the regular (non-netinst) ISO.

Use unetbootin to make a USB flash drive image for this. Go into the BIOS on the X1 Yoga, enable F12 for boot device selection (just because), turn off secure boot, maybe enable diagnostic boot as well. No need to allow legacy BIOS installs, Debian will work just fine with uEFI (unlike FreeBSD where you need to use the 10.3-Beta or 11 memstick). Go through the install like you usually do. Your ethernet (if you have it) will be detected (again, unlike in FreeBSD).

Sound, APCI (suspend, hibernate, and battery status) and video card should all be working out of the box.


Wireless

Upgrade your kernel to 4.4.1 from the ubuntu PPA:
  http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.4.1-wily/
This is per notes about a typo in the iwlwifi driver at
 https://bbs.archlinux.org/viewtopic.php?id=206831
Looking at the kernel source, 4.2.7 has the fix as well, but might as well go with the latest stable release of the kernel if we're upgrading.

You'll also need to upgrade the firmware, or your Wifi will not be recognized. There is a debian package in backports for this:
 https://packages.debian.org/jessie-backports/firmware-iwlwifi


Skylake P-State Fix

If you rebooted excitedly into your new kernel without following the rest of these steps, you're likely looking at a blank screen. That's because of a skylake p-state bug reported here:
 https://www.reddit.com/r/thinkpad/comments/410haw/yoga_260_wont_boot_ubuntu_with_kernel_4244_but/

This is because the kernel needs a command line parameter to not totally crap itself when it encounters Skylake's poor implementation of pstate.

To fix this, change the cmdline in /etc/default/grub to:
  GRUB_CMDLINE_LINUX_DEFAULT='intel_pstate=no_hwp quiet'

Don't forget to run update-grub when you're done.

Hopefully this will go away in 4.5; according to a commenter, that's what the kernel guys are trying for.


i915 Xorg Video fix

Of course, the fancy new kernel hosed your X windows, didn't it?

Not sure why there's such a tight coupling there, but never mind. This one's an easy fix, per http://comments.gmane.org/gmane.linux.debian.user/508779 . Download (and install) a new version of the xserver-xorg-video-intel package from backports:

https://packages.debian.org/jessie-backports/xserver-xorg-video-intel


Touchscreen

The touchscreen is recognized and configurable in X Windows, but does not respond to touch or stylus events. A bug report is open at the linuxwacom project.

The touchscreen (+ stylus) works out of the box once the firmware update is installed (via windows, sadly,so don't pave the drive until you've updated firmware). Make sure to perform a hard reset (60 sec with a paperclip in the bottom of the laptop) after the upgrade.

To disable the touchpad when entering tablet mode (note: the keyboard will be disabled by  the BIOS), create the file /etc/acpi/events/thinkpad-tablet-touchpad-off with the following contents:

event=ibm/hotkey LEN0068:00 00000080 000060f0
action=/usr/local/bin/touchpad_disable.sh

You can verify the hotkey parameter by running acpi_listen and folding the display back to tablet position.

Next, create the file /usr/local/bin/touchpad_disable.sh with the following contents:

export XAUTHORITY=`ls -1 /home/*/.Xauthority | head -n 1`

export DISPLAY=":`ls -1 /tmp/.X11-unix/ | sed -e s/^X//g | head -n 1`"

tp_dev='SynPS/2 Synaptics TouchPad'

state=`xinput list-props "$tp_dev" | grep 'Device Enabled' | cut -d':' -f2 | tr -d '\t '`

if [ $state -eq 1 ]

then

  xinput disable "$tp_dev"

else

  xinput enable "$tp_dev"

fi

You will need to give root access to the X server session for this. The quickhack version is to add xhost + & to ~/.xsessionrc, but it's better to do something like +root@localhost..

The Acer BMA150 accelerometer is detected as a joystick device, so various /sys/bus/iio -based screen orientation scripts like thinkpad-yoga-scripts won't work. An alternative is to define a Window Manager screen edge event that invokes a script to cycle through screen orientation rotations:

#!/bin/sh
# script to rotate screen (counter-clockwise) based on current orientation

conn_line=`xrandr | grep ' connected'`
dev=`echo "$conn_line" | cut -d' ' -f 1`
orient=`echo "$conn_line" | cut -d' ' -f 5`

case $orient in
  '(normal' )
    xrandr --output $dev --rotate left
    ;;
  'left' )
    xrandr --output $dev --rotate inverted
    ;;
  'inverted' )
    xrandr --output $dev --rotate right
    ;;
  'right' )
    xrandr --output $dev --rotate normal
    ;;
  * )
    xrandr --output $dev --rotate normal
    ;;
esac

Some other approaches are discussed in this Manjaro Linux post.

Fingerprint reader

Is not supported by fprint. USB ID: 138a:0090 (Validity, no product string in usb-devices).


Camera

Works out of the box. Driver is uvcvideo. VLC mirrors it without any problems:

vlc v4l:// :v4l-dev="/dev/video0" :v4l-adev="/dev/audio"


FreeBSD

You need to use a 10.3 (BETA3 or more current) UEFI memstick image to do the install with, of course, the OneLink ethernet adapter connected. Presently, no support for wifi or Xorg support (perhaps in 11?). To boot, add an entry in /etc/grub.d/40_custom as follows:

menuentry "FreeBSD 10.3-BETA3" {
  insmod chain
  set root=(hd0,gpt10)
  chainloader (hd0,gpt10)/boot/loader.efi
}

...replacing gpt10 with the partition number where FreeBSD was installed. This starts counting from 1, so the example here is the tenth partition on the first hard drive (hd0).

Note that for update-grub to correctly recognize the FreeBSD partition (and therefore find loader.efi), you should provide an fstab entry to specify the UFS partition type:

/dev/sda10      /home/bsd       ufs    ro,noauto,ufstype=ufs2       0       0

perf-backed disassembly

Since 2.6.31 or thereabouts, the Linux kernel has come with a built-in performance counter known as perf.

The common form of perf is well-known to be useful in gathering performance statistics on a running program:


bash$ perf stat -cv ./a.out 


cache-misses: 11313 2020574449 2020574449
cache-references: 62031796 2020574449 2020574449
branch-misses: 17909 2020574449 2020574449
branches: 606684832 2020574449 2020574449
instructions: 6324531571 2020574449 2020574449
cycles: 6408533747 2020574449 2020574449
page-faults: 304 2019963367 2019963367
CPU-migrations: 7 2019963367 2019963367
context-switches: 205 2019963367 2019963367
task-clock-msecs: 2019963367 2019963367 2019963367


 Performance counter stats for './a.out':

             11313 cache-misses             #      0.006 M/sec
          62031796 cache-references         #     30.709 M/sec
             17909 branch-misses            #      0.003 %    
         606684832 branches                 #    300.344 M/sec
        6324531571 instructions             #      0.987 IPC  
        6408533747 cycles                   #   3172.599 M/sec
               304 page-faults              #      0.000 M/sec
                 7 CPU-migrations           #      0.000 M/sec
               205 context-switches         #      0.000 M/sec
       2019.963367 task-clock-msecs         #      0.996 CPUs 


        2.027948307  seconds time elapsed

The  events to be recorded can be specified with the -e option in order to refine the output:

bash$ perf stat -e cpu-clock -e instructi

ons  

 Performance counter stats for './a.out':

       2026.748812 cpu-clock-msecs         

        6324293589 instructions             #      0.000 IPC  

        2.032519896  seconds time elapsed

A list of available events can be obtained via perf list:

bash$ perf list | head

List of pre-defined events (to be used in -e):

  cpu-cycles OR cycles                       [Hardware event]

  instructions                               [Hardware event]

  cache-references                           [Hardware event]

  cache-misses                               [Hardware event]

  branch-instructions OR branches            [Hardware event]

  branch-misses                              [Hardware event]

  bus-cycles                                 [Hardware event]

The perf toolchain also includes the utility perf top, which can be used to monitor a single process, or which can be used to monitor the kernel:

bash$ sudo perf top 2>/dev/null

-------------------------------------------------------------------------------

   PerfTop:       0 irqs/sec  kernel:-nan%  exact: -nan% [1000Hz cycles],  (all, 4 CPUs)

-------------------------------------------------------------------------------

             samples  pcnt function               DSO

             _______ _____ ______________________ __________________

               77.00 39.3% intel_idle             [kernel.kallsyms] 

               13.00  6.6% __pthread_mutex_unlock libpthread-2.13.so

               13.00  6.6% pthread_mutex_lock     libpthread-2.13.so

               12.00  6.1% __ticket_spin_lock     [kernel.kallsyms] 

                7.00  3.6% schedule               [kernel.kallsyms] 

                6.00  3.1% menu_select            [kernel.kallsyms] 

                6.00  3.1% fget_light             [kernel.kallsyms] 

                6.00  3.1% clear_page_c           [kernel.kallsyms] 

Where things start to get interesting, however, is with perf record. This utility is generally used along with perf report to record the performance counters of a process, and review them later.

This can be used, for example, to generate a call graph:

bash$  perf record -g -o /tmp/a.out.perf ./a.out

[ perf record: Woken up 1 times to write data ]

[ perf record: Captured and wrote 0.148 MB /tmp/a.out.perf (~6461 samples) ]

bash$ perf report -g -i /tmp/a.out.perf

# Events: 1K cycles

#

# Overhead        Command  Shared Object  Symbol

# ........  .............  .............  ......

#

    99.90%          a.out  a.out          [.] main

            |

            --- main

                __libc_start_main

     0.10%          a.out  [l2cap]        [k] 0xffffffff8103804a

            |

            --- 0xffffffff8105f438

                0xffffffff8105f675

...

Once perf data has been recorded, the perf annotate utility can be used to display a disassembly of the instructions that were executed:

bash$  perf annotate -i /tmp/a.out.perf |more

------------------------------------------------

 Percent |      Source code & Disassembly of a.out

------------------------------------------------

         :

         :

         :

         :      Disassembly of section .text:

         :

         :      0000000000400554

:

    0.00 :  400554:       55                      push   %rbp
    0.00 :  400555:       48 89 e5                mov    %rsp,%rbp
    0.00 :  400558:       48 81 ec 30 00 0c 00    sub    $0xc0030,%rsp
    0.00 :  40055f:       48 8d 85 d0 ff fb ff    lea    -0x40030(%rbp),%rax
    0.00 :  400566:       ba 00 00 04 00          mov    $0x40000,%edx
    0.00 :  40056b:       be 00 00 00 00          mov    $0x0,%esi
    0.00 :  400570:       48 89 c7                mov    %rax,%rdi
    0.00 :  400573:       e8 b0 fe ff ff          callq  400428 <memset@plt>
    0.00 :  400578:       c7 45 fc 00 00 00 04    movl   $0x4000000,-0x4(%rbp)

    ...

    4.21 :  4006a5:       8b 45 d0                mov    -0x30(%rbp),%eax
   15.54 :  4006a8:       83 c0 01                add    $0x1,%eax
    4.97 :  4006ab:       89 45 d0                mov    %eax,-0x30(%rbp)
    4.87 :  4006ae:       8b 45 d0                mov    -0x30(%rbp),%eax
   17.79 :  4006b1:       83 c0 01                add    $0x1,%eax
    4.36 :  4006b4:       89 45 d0                mov    %eax,-0x30(%rbp)
    4.72 :  4006b7:       48 83 45 f0 01          addq   $0x1,-0x10(%rbp)
    0.00 :  4006bc:       48 8b 45 f0             mov    -0x10(%rbp),%rax

    ...

As to be expected from Torvalds and company, the utilities include a number of options for generating parser-friendly output, limiting reporting to specified events and symbols, and so forth. Check the man pages for details.

Free as in...

Finally got sick of building custom Linux kernels just to change CONFIG_HZ from the inane default of 250 to something that makes the 10ms timer in my (proprietary) device driver work reliably (instead of firing 83 times a second). Switched to hi-resolution timers, and immediate encountered this:

FATAL: modpost: GPL-incompatible module my_module.ko uses GPL-only symbol 'hrtimer_cancel'


Turns out, after reading stuff like http://www.linuxdevices.com/articles/AT9161119242.html and http://www.linuxdevices.com/articles/AT5041108431.html, that the lunatics have taken over the asylum: specific kernel subsystems can be restricted so that only GPL modules can call them.

This is ludicrous: why should GPL code care who calls it? This has nothing to do with distribution; this is *usage*.

Not to mention entirely unlike the "free as in speech" ethos that the FSF claims to support. "Free speech" generally doesn't imply "say anything you like, just don't say it in kernel mode!".

Between this GPL nonsense and the changing of the CONFIG_HZ default value in a minor release, the Linux kernel is proving itself quite unreliable. I may have to move this entire product over to FreeBSD.