Nexus 7 Kernel Notes

This is a collection of notes about the nexus 7 kernel relevant to discussions planned for UDS-R.

Kernel Delta

The nexus 7 kernel is based off of the 3.1.10 stable kernel with approximately 6100 additional non-merge commits. Many (likely most) of these are related to hardware support, including support for the tegra 3 SoC, nexus 7 board, and additional devices.

The following sections outline hardware support in the nexus 7 kernel that is not in mainline Linux as of the 3.7 merge window. Note that the list is a work in progress -- some hardware may be missing, and some drivers in the list may not actually be needed for the nexus 7.

Also noteworthy is the fact that in some places Google has squashed together a bunch of individual commits into a single commit. Therefore the raw change counts below may not be representative of the actual number of changes.

Tegra 3 SoC Support

• Trusted foundations driver: Probably related to DRM (as in digital rights management, not kernel modesetting). ogra reports that the nexus 7 will not boot without this driver.
• Thermal support
• Pin muxing: This might be present upstream, but it's certainly different than in the kernel from Google. Could also be expected that pin muxing is done by the bootloader.
• SPI
• Display/graphics
• PMU
• USB: Possible differences in support, needs a closer look.
• Watchdog timer
• tegra-avp (audio/video processing)
• tegra_camera
• tegra-se (security engine): Crypto acceleration. There is a separate driver for AES acceleration that's present both upstream and in the kernel from Google.
• tegra30-dam: This is related to audio.
• tegra30-spdif
• tegra30-dit: This is related to audio.
• tegra-pcm-audio
• tegra30-hda: Looks related to HDMI, likely audio.
• tegra-sensor
• Video capture: For camera support.
• tegra-baseband: For baseband modem support.
• tegra-cryptodev: Provides device node access to AES acceleration.

Device Drivers

• max17048: Gas gauge chip for battery status information.
• bq27541-battery: Gas gauge chip for battery status information.
• smb347: Battery charger chip. There is a driver upstream, but it's completely different from the one in Google's kernel.
• rt5640: DSP
• rt5639: Audio codec
• bcm4330_rfkill: Looks like a driver for implementing rfkill support for the wireless devices based off of a GPIO pin.
• ektf3k: Touchscreen
• max77663: PMIC
• bcmdhd: Broadcom full-MAC wireless device. Possibly supported upstream by brcmfmac.
• switch_class/switch_gpio: Provide sysfs/uevent interface to userspace for hw switches.
• ltr558als: Ambient light sensor
• inv-ami305: Compass
• inv_mpu: Probably an accelerometer
• mi1040: Camera sensor
• nct1008: Temperature monitoring device
• max1749: Vibrator
• max77663: Multi-function device (PMIC, RTC, etc.)
• ricoh583: Multi-function device (PMIC, RTC)
• tps8003x: Multi-function device (PMIC, RTC)

Other Significant Changes

• A good number of the non-arch and non-driver patches appear to be backports, although it's unclear how many. A quick survey of some of the changes to core kernel code seems to indicate that most of those changes are backports.
• Google's kernel has extensive modifications to the networking code. Some of these are around security, others add features that Android userspace uses which are not likely to be needed for Ubuntu. However some appear to be legitimate bug fixes that may not be upstream.
• Google kernel exports chip and pcb ids via sysfs. Might not be needed, unless we need to account for hardware version differences in userspace somehow.
• Android drivers. These are supported to various degrees in mainline under the staging tree, but we shouldn't need most of them if we need any at all. Some drivers are not in staging however:

  • switch_class/switch_gpio: Provides sysfs/uevent interface to userspace for hw switches connected to GPIOs. Note: This has likely been superseded upstream by the extcon driver.

  • gpio_output/gpio_axis/gpio_event/gpio_input/gpio_matrix
  • keychord: Driver to provide notifications when specified key combinations are pressed.

Breakdown of changes on top of 3.1.10

Paths with no changes were omitted.

• Total non-merge commits on top of 3.1.10: 6069
• Broken down by subdirectories
  • /arch: 3130
    • /arm: 3112
    • /ia64: 4
    • /s390: 2
    • /sh: 1
    • /sparc: 9
    • /x86: 8
  • /block: 4
  • /crypto: 5
  • /Documentation: 17
  • /drivers: 2655
    • /base: 110
    • /bluetooth: 12
    • /char: 3
    • /cpufreq: 52
    • /cpuidle: 1
    • /crypto: 49
    • /dma: 8
    • /gpio: 24
    • /gpu: 38
    • /hid: 5
    • /hwmon: 37
    • /i2c: 45
    • /infiniband: 1
    • /input: 107
    • /iommu: 89
    • /leds: 1
    • /md: 6
    • /media: 188
    • /mfd: 108
    • /misc: 101
    • /mmc: 116
    • /mtd: 15
    • /net: 219
    • /nfc: 5
    • /oprofile: 1
    • /pci: 1
    • /power: 61
    • /regulator: 101
    • /rtc: 57
    • /s390: 1
    • /scsi: 4
    • /spi: 34
    • /ssb: 1
    • /staging: 48
    • /switch: 2
    • /tty: 51
    • /usb: 316
    • /video: 661
    • /w1: 2
    • /watchdog: 13
  • /fs: 27
    • /ecryptfs: 5
    • /ext4: 2
    • /fat: 1
    • /fuse: 1
    • /nfs: 2
    • /nilfs2: 1
    • /partitions: 4
    • /proc: 5
    • /xfs: 2
    • /yaffs2: 3
  • /include: 540
  • /init: 3
  • /kernel: 74
  • /lib: 3
  • /mm: 14
  • /net: 88
    • /sctp: 2
    • /sunrpc: 1
    • /wireless: 9
    • /xfrm: 1
  • /security: 8
  • /sound: 238
  • /virt: 3