Gentoo Linux on the ASUS TF700

This page holds resources useful in installing and using Gentoo Linux on the ASUS TF700, also known as the Transformer Pad Infinity.

Warning: If you make a mistake trying to install Gentoo, your tablet may become unusable! These resources are provided in the hope that they will be useful, but with no warranty; use them at your own risk. (If you don't completely understand the instructions below, this page is not for you.)

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Overview

The procedure and files below allow installation of Gentoo Linux on the ASUS TF700 tablet. This install is performed directly onto the Android /data filesystem, allowing Gentoo and Android to coexist on the same device without repartitioning the internal storage. (On the Gentoo side, this is accomplished through the hack of doing a chroot() to the Linux install directory before running /sbin/init.)

Overall, the state of (this image of) Gentoo on the TF700 could be described as "minimally functional"; it works at a basic level, but doesn't come close to replacing an ordinary laptop PC. (Which is a shame; even if not up to Linus Torvalds standards, the high-resolution display still far outstrips current laptop offerings, and it has multitouch support as well.)

These instructions worked for my Japanese-model device, starting with firmware 9.4.5.26 installed; I have no idea how well they work on other models or firmware versions.

What works

• Booting: Gentoo can boot successfully to a login prompt.
• Framebuffer console, though scrolling is slow.
• Wireless LAN: Available through the bcmdhd module.
• Sound: Works for the headphone jack only, and you need to explicitly unmute it with alsamixer. Also be sure to turn the PCM output level down to a reasonable value (70-80 on my device) so you don't blow your ears out!
• SD card slot (but see below about I/O speed).
• The adbd program is provided through a TF700-specific package, dev-android/adbd. If enabled via /etc/init.d/adbd start (or added to the startup service list with rc-update add adbd default), you can connect the TF700 to a PC and use adb shell as with Android. Note that adbd gives a root shell, so use with care.

What doesn't work

• X Window System: I was unable to get X running stably. I succeeded in getting the X server to start, and I could get the X display to show for an instant by starting and terminating an X client (I used xev), but nothing else seemed to work.
• Screen unblanking: If the screen blanks (either from the standard blanking timeout or from writing 0 to /sys/class/backlight/pwm_backlight/brightness), you have to press the power or volume up/down buttons to turn it back on; pressing keys on the keyboard won't work. Sometimes the screen fails to unblank and you have to hard-reboot by holding down the power button (I haven't tested whether adb shell still works in this case).

Other pain points

• Dual booting: Since there is (to my knowledge) no bootloader software that supports the TF700, the only way to switch between Gentoo and Android is by manually overwriting the boot partition.
• Storage I/O is extremely slow: I measured only 20MB/sec for the internal flash storage, and only 10MB/sec for the external SD card slot (using an SD card rated at 30MB/sec). Operations which cover large numbers of files, such as extracting the Linux kernel source, can take tens of minutes to complete.
• Keyboard layout: The TF700's keyboard layout is inconvenient when using standard Linux applications. In particular:
  • The top row of keys (which would be function keys on a PC) are only labeled with symbols, and also are not split into groups as on a PC keyboard (F1-F4, F5-F8, and so on) so you can't tell by feel which Fn key number a given key corresponds to.
  • There's no "delete" key (though potentially one of the top row keys could be reassigned to that function).
  • The up-arrow key intrudes on the bottom alphabetic row of keys, next to the right shift key. I frequently find myself accidentally hitting up-arrow instead of shift.
• Weight balance: Since the bulk of the TF700's electronics are in the tablet rather than the dock, the device is somewhat top-heavy when docked and used in a typical laptop configuration. This isn't a problem when the TF700 is sitting on a table, but it tends to fall over backwards when sitting on a lap, cushion, or other soft surface.
• Sharp edges: If you're not careful when lifting open the screen from its folded position, you can cut your finger on the edge of the metal casing.

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Installation procedure

1. Unlock the TF700 bootloader using the Android app provided by ASUS. Warning: This will void your warranty! To download:
   1. Go to the ASUS download site.
   2. From the "OS:" dropdown, select "Android".
   3. Expand the "Utilities" category.
   4. Download "Unlock Device App".
   Note that you need to be connected to the Internet for the unlock tool to work. Also, as of this writing the app is described as only working with Android 4.0 (Ice Cream Sandwich), so you may not be able to use it if you upgrade to Android 4.1 (Jellybean).
2. Install a custom recovery tool, such as TWRP, which allows you to connect with adb shell to get a root shell. (For the initial installation, it is also possible to exploit a bug in the Android boot sequence to get a root-enabled shell; in that case, you can use an Android terminal emulator app and perform the initial installation in Android itself. However, having an adb-enabled recovery tool is strongly recommended as a way to recover from a bad kernel install or other errors.)
3. Boot into the recovery tool (hold the power and volume-down buttons until the screen displays "Checking for RCK..." in the upper-left corner, then release both buttons and press the volume-up button).
4. Connect the TF700 to a PC with the USB cable, and verify that you can get a shell with adb shell.
5. Download the Linux image (linux-root.tar.gz) and the tar binary, and copy them to /data/local on the device:
   adb push linux-root.tar.gz /data/local
   adb push tar /data/local
6. In adb shell, expand the Linux image in the /data directory:
   /data/local/tar Cxzvfp /data /data/local/linux-root.tar.gz
7. Check that the Linux image was successfully unpacked on the device:
   ls /data/linux-root
   You should see typical top-level directories for a Linux install (bin, dev, etc, and so forth).
8. Verify the location of the boot partition:
   dd bs=512 skip=23552 count=1 </dev/block/mmcblk0 2>/dev/null | dd bs=8 count=1 2>/dev/null; echo
   This should output the string "ANDROID!". If it does not, stop here; you need to find the sector offset of the boot partition on your device and use that in place of "23552" in these instructions.
9. Make a backup copy of your Android boot image:
   dd bs=512 skip=23552 count=16384 </dev/block/mmcblk0 >/data/linux-root/boot/boot-android.img
10. Install the Gentoo boot image:
    dd bs=512 seek=23552 count=16384 </data/linux-root/boot/boot-gentoo.img >/dev/block/mmcblk0
    (You can also use this command to restore the original Android boot image, allowing you to boot into Android again; just change "boot-gentoo" to "boot-android".)
11. In adb shell, run the sync command to ensure that all changes have been written to disk.
12. Reboot the tablet, either using the recovery interface or by running the command adb reboot from your PC. Gentoo Linux should now boot up.

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Default configuration

The Linux image installed through the instructions above includes a single user account, "tf700". The password for both this user account and the root (superuser) account is also "tf700". Naturally, you should change these if you intend to make any significant use of your Gentoo install.

The Linux image includes only basic system packages, plus a few packages specific to the TF700. Those packages are:

• dev-android/adbd: The adbd program which responds to USB requests from adb on a PC, along with an init script to start and stop the daemon.
• dev-android/mkbootimg: A utility program to create an Android boot image, used by the tf700-simpleboot script when installing a kernel.
• sys-boot/tf700-simpleboot: A trivial boot program which mounts the /data filesystem and does a chroot() to the root of the Linux image (/data/linux-root), then calls the standard /sbin/init program to boot Linux normally. The package also includes a tf700-simpleboot script which automates the process of creating a boot image from this boot program and an arbitrary kernel.
• sys-kernel/tf700-sources: Linux kernel source code, with patches for the TF700. This is a merge of the kernel source code from the ASUS firmware version 9.4.5.30, the latest (as of this writing) Android kernel source for kernel 2.6.39.4 from Google (AOSP packages kernel/tegra), and a few custom changes (see the patches downloaded by the package).

The packages above are available from a Portage overlay at http://achurch.org/hg/portage-tf700, which is preinstalled via the layman tool (the overlay description file can be found at http://achurch.org/portage-tf700-layman.xml).

The image also includes a custom keymap, located at /usr/local/share/keymaps/tf700.map and loaded by /etc/conf.d/keymaps. This keymap:

• Maps the top row of keys to Esc and F1-F15. (The lock key is left unmapped.)
• Maps the Home, Search, and Menu keys on the bottom row to Alt.

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Updating and restoring the kernel

If you build a new kernel, you need to install it to the boot partition before it will be recognized. The tf700-simpleboot script takes care of this; run tf700-simpleboot install path-to-kernel to install the new kernel (located at path-to-kernel) to the boot partition.

tf700-simpleboot does not provide any facility for a backup kernel, so if the kernel you install fails to boot, you will need to use the tablet's recovery mode to reinstall a known-good kernel.

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