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ASUS C302

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The Asus C302 (also known as Asus C302C and Asus C302CA) is a Chromebook, which can have Linux installed. Here are some pointers on the smooth running of Arch Linux.

Installation

Add acpi_osi=Linux intel_iommu=on,igfx_off to your kernel parameters.

intel_iommu=on,igfx_off is from BBS#228604, to prevent the following error from appearing in the output of dmesg: 

[drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU pipe A FIFO underrun

The CPU is an Intel Core M3, so install intel-ucode.

Kernel Modules

In e.g. /etc/modprobe.d/skylake.conf 

# Needed for the nau8825 kernel sound modules to initialize
blacklist snd_hda_intel

options tpm_tis interrupts=0

Note: this does not seem necessary (anymore?), audio also works with snd_hda_intel and alsa-firmware, as described under #Sound.

Screen

The screen is 12.5 inches diagonally. At 1920x1080 resolution, this is 176 DPI, which is HiDPI.

In ~/.xinitrc, to set the screen dimensions (measured in millimetres): 

xrandr --fbmm 277x156

Vsync

For proper vsync (including e.g. fullscreen Youtube in Firefox) in XFCE, install xfwm4-gitAUR, and enable XFCE's compositor.

Proper vsync also requires xf86-video-intel, rather than modesetting.

In /etc/X11/xorg.conf.d/20-intel.conf 

Section "Device"
    Identifier "Intel Graphics"
    Driver "intel"
EndSection

Screen Flipping

To use the laptop in tent mode, the following script will flip both the screen and touch input: 

#!/bin/dash

set_normal() {
	r="normal"
	ctm="1 0 0 0 1 0 0 0 1"

}

set_upside_down() {
	r="inverted"
	ctm="-1 0 1 0 -1 1 0 0 1"
}

line=$(xrandr | grep '^eDP.* connected ')
screen=$(printf "%s" "$line" | cut -d" " -f1)

if $(printf "%s" "$line" | grep -q ' inverted (normal') ; then
	set_normal
else
	set_upside_down
fi

xrandr --output "$screen" --rotate "$r"
xinput set-prop "Elan Touchscreen" "Coordinate Transformation Matrix" $ctm

Keyboard

To use the top row of Chromebook keys as useful keys in xorg, use e.g.:

In ~/.Xmodmap 

keycode   9 = Escape NoSymbol Escape
keycode  22 = BackSpace BackSpace BackSpace BackSpace Delete NoSymbol Delete
keycode  37 = Control_L NoSymbol Control_L
keycode  50 = Shift_L NoSymbol Shift_L
keycode  66 = Caps_Lock NoSymbol Caps_Lock
keycode  67 = Home F1 Home F1 F1 F1 XF86Switch_VT_1
keycode  68 = End F2 End F2 F2 F2 XF86Switch_VT_2
keycode  69 = Prior F3 Prior F3 F3 F3 XF86Switch_VT_3
keycode  70 = Next F4 Next F4 F4 F4 XF86Switch_VT_4
keycode  71 = Delete F5 Delete F5 F5 F5 XF86Switch_VT_5
keycode  72 = XF86MonBrightnessDown F6 XF86MonBrightnessDown F6 F6 F6 XF86Switch_VT_6
keycode  73 = XF86MonBrightnessUp F7 XF86MonBrightnessUp F7 F7 F7 XF86Switch_VT_7
keycode  74 = XF86AudioMute F8 XF86AudioMute F8 F8 F8 XF86Switch_VT_8
keycode  75 = XF86AudioLowerVolume F9 XF86AudioLowerVolume F9 F9 F9 XF86Switch_VT_9
keycode  76 = XF86AudioRaiseVolume F10 XF86AudioRaiseVolume F10 F10 F10 XF86Switch_VT_10
keycode 111 = Up Up Up Up Prior Prior
keycode 112 = Prior NoSymbol Prior
keycode 113 = Left Left Left Left Home Home
keycode 114 = Right Right Right Right End End
keycode 115 = End NoSymbol End
keycode 116 = Down Down Down Down Next Next
keycode 117 = Next NoSymbol Next
keycode 118 = Insert NoSymbol Insert
keycode 119 = Delete NoSymbol Delete
keycode 124 = XF86PowerOff NoSymbol XF86PowerOff
keycode 167 = XF86Forward NoSymbol XF86Forward
keycode 182 = XF86Close NoSymbol XF86Close
keycode 191 = XF86ScreenSaver NoSymbol XF86ScreenSaver

(This list can be pruned.)

~/.Xmodmap will be loaded by /etc/X11/xinit/xinitrc, which effectively runs: 

xmodmap ~/.Xmodmap

Keyboard Backlight

To be able to change the keyboard backlight brightness as a normal user, run as root: 

b="/sys/devices/platform/GOOG0002:00/leds/chromeos::kbd_backlight/brightness"
chgrp users "$b" &&
chmod 660 "$b" &&
echo 6 > "$b"

It is a value between 0 (off) and 100 (full brightness). The default on ChromeOS is 25. 6 is a reasonable lower value.

ChromeOS is able to disable the keyboard backlight, when the keyboard is not being used - that functionality does not appear to be available in the Linux kernel, but can be replicated in a simple script, with the aid of xprintidle, e.g.: 

#!/bin/dash

set_keyboard_backlight() {
	printf "%s" "$1" > "/sys/devices/platform/GOOG0002:00/leds/chromeos::kbd_backlight/brightness"
	b="$1"
}

b=0

while true ; do
	pgrep ^Xorg > /dev/null || exit 0

	seconds_to_sleep=10
	idle_millis=$(xprintidle)
	if [ "$idle_millis" -gt 10000 ] ; then
		nb=0
		seconds_to_sleep=5
	else
		nb=25
		seconds_to_sleep=15
	fi

	if [ "$nb" -ne "$b" ] ; then
		set_keyboard_backlight "$nb"
	fi

	echo "nb=$nb, sleeping for $seconds_to_sleep"
	sleep "$seconds_to_sleep"
done

Touchpad

As of libinput 1.12.0-2, the touchpad works nicely with all of:

  • Tapping:
    • 1-finger tap = "left" button
    • 2-finger tap = "right" button
    • 3-finger tap = "middle" button
  • Clickpad (clicking the lower portion of the touchpad):
    • Left side = "left" button
    • Right side = "right" button
    • Middle = "middle" button

Mouse

Due to the limited amount of USB ports, a Bluetooth mouse is a good option. The Logitech M590 mouse works great.

Run "bluetoothctl power on &" at startup, e.g. in ~/.xinitrc

In e.g. /etc/X11/xorg.conf.d/99-mouse.conf 

Section "InputClass"
    Identifier "Logitech M590"
    MatchIsPointer "on"
    MatchDevicePath "/dev/input/event*"
    Driver "libinput"
    Option "AccelProfile" "flat"
EndSection

Then, the "speed" of the mouse can be set using the XFCE GUI, in "Settings - Mouse", setting the "acceleration" to e.g. 2.0

Sound

The laptop should be able to play sound via HDMI (untested), built-in speaker, headphone jack, or Bluetooth headsets.

For Bluetooth, follow the standard Bluetooth and Bluetooth headset setup.

Built-in speaker and headphone jacks work with ALSA after installing the alsa-utils (optional?) and alsa-firmware packages, and then rebooting to ensure the firmware is loaded.

ALSA can also be used as the output sink for the PulseAudio (untested) and Pipewire sound servers.

More information here:


Troubleshooting

When succesful, lspci -v -s 00:1f.3 should show: 

00:1f.3 Multimedia audio controller: Intel Corporation Sunrise Point-LP HD Audio (rev 21)
	DeviceName: Multimedia audio controller
	Flags: bus master, fast devsel, latency 64, IRQ 132, IOMMU group 7
	Memory at 9112c000 (64-bit, non-prefetchable) [size=16K]
	Memory at 91110000 (64-bit, non-prefetchable) [size=64K]
	Capabilities: [50] Power Management version 3
	Capabilities: [60] MSI: Enable+ Count=1/1 Maskable- 64bit+
	Kernel driver in use: snd_soc_avs
	Kernel modules: snd_soc_avs, snd_hda_intel

And aplay -l shows: 

**** List of PLAYBACK Hardware Devices ****
card 0: HDMI [AVS HDMI], device 0: HDMI1 (*) []
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: HDMI [AVS HDMI], device 1: HDMI2 (*) []
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: HDMI [AVS HDMI], device 2: HDMI3 (*) []
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: MAX98357A [AVS I2S MAX98357A], device 0: Built-in Speakers (*) []
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 4: NAU8825 [AVS I2S NAU8825], device 0: Headset (*) []
  Subdevices: 1/1
  Subdevice #0: subdevice #0

Here, MAX98357A is the built-in speaker and NAU8825 is the headphone audio port.

Verify playback works, e.g. with: 

aplay -D default:CARD=MAX98357A -i example.wav

ALSA

To set audio to a sensible level, run in ~/.xinitrc: 

amixer -q -c0 sset Headphone 70% &

PulseAudio

To prevent audio "clicks", comment out "load-module module-suspend-on-idle" in /etc/pulse/default.pa and /etc/pulse/system.pa

Coil Whine

There is occasional coil whine, which can be greatly reduced by running: 

printf "1" > /sys/devices/system/cpu/intel_pstate/no_turbo