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ludiazv cddadc1f4b DT overlay support 
Experimental feature to include DT overlays and custom boot args
2023-05-30 13:27:31 +02:00

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meta-sunxi

Official sunxi OpenEmbedded layer for Allwinner-based boards.

This layer depends on the additional layers:

Tested with core-image-base.

Maintainers:

Community

You can reach community + ask your question on gitter: https://matrix.to/#/#meta-sunxi:gitter.im

Kernel / U-Boot Version

Most Allwinner devices and hardware are supported in mainline kernel and U-Boot, so this layer builds mainline by default.

Legacy sunxi Kernel / U-Boot

There is a custom U-Boot and Kernel version for sunxi devices which includes some special drivers not mainlined. These versions are rather old (3.4 for kernel and 2014.04 for U-Boot), but may support more functions and devices than current mainline.

If you want to switch back to sunxi versions for some reasons (no device tree available, unsupported hardware), either:

  • change the file conf/machine/include/sunxi.inc to include the following block

  • edit your conf/local.conf to add the following block

      PREFERRED_PROVIDER_u-boot="u-boot-sunxi"
  PREFERRED_PROVIDER_virtual/bootloader="u-boot-sunxi"
  PREFERRED_PROVIDER_virtual/kernel="linux-sunxi"
  KERNEL_DEVICETREE = ""

If you already have built the mainline versions it might be necessary to reset the build directories with:

bitbake -c clean virtual/kernel virtual/bootloader

Mainline Kernel / U-Boot

For mainline kernel we have now support for latest LTS and stable. By default we use latest LTS. If you would like to change version please update PREFERRED_VERSION_linux-mainline in:

When using mainline kernel ≥ 5.2 it is now possible to use the mainline graphics drivers lima and panfrost, instead of the mali driver provided by ARM. To enable open source mainline graphics support add the following line in your local.conf:

MACHINEOVERRIDES .= ":use-mailine-graphics"

Performance

The default machine settings are meant to be the lowest common denominator, maximizing generality. Significantly better performance (2x-3x) can be achieved with the following settings:

Allwinner A20

For Allwinner A20 (Cubieboard2/CubieTruck), the following tuning options are recommended:

Enable hardfloat, thumb2 and neon capabilities

DEFAULTTUNE = "cortexa7hf-neon-vfpv4"

This tuning profile takes advantage of the Allwinner A20 hardfloat, neon and vfpv4 capabilities.

Change CPU governor to ondemand, and tune settings

echo ondemand > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
echo 336000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq
echo 912000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
#More aggressive
#echo 1008000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
echo 40 > /sys/devices/system/cpu/cpufreq/ondemand/up_threshold
echo 200000 > /sys/devices/system/cpu/cpufreq/ondemand/sampling_rate

This code changes the default CPU governor from fantasy to ondemand, and tunes its settings, as recommended at http://linux-sunxi.org/Cpufreq

For additional discussion, see https://github.com/linux-sunxi/meta-sunxi/issues/25

Custom boot environment & devicetree overlay suppport

The layer provide a basic custom enviroment for linux mainline that enables:

  • Custom boot argument to be passed to the kernel.
  • Basic devicetree overlay support.

By default this features are disabled and have to be activated including this the bitbake configuration (e.g. local.conf):

DISTRO_FEATURES:append = " sunxi-env"

This feature instruct the layer to deploy the file /boot/sunxienv.txt that is loaded during boot customize kernel boot command line.

DT Overlay support

To enable overlays the following line must be activated in bitbake configuration (e.g. local.conf):

SUNXI_OVERLAYS_ENABLE:append = " <space separeted list with the desired overlay names without .dts>"

The layer includes a common set for DT overalys organized by family. The list can be found in the following path meta-sunxi/recipes-bs/sunxi-overlays/files/<socfamily>/<dts file>

Once activated the following content will be added to yout image in the boot partition:

/boot/dtbo/*.dbto (all compiled overlays selected in SUNXI_OVERLAYS_ENABLE)
/boot/sunxienv.txt (uboot config file with the full list of devicetree overlays)

/boot/sunxienv.txt can be modified after the build to activate or deactive the overlays on boot to provide runtime flexibility or for debugging. A .dbto file can be also loaded at runtime if the kernel supports it via sysfs interface using cat [dbto file] > /sys/kernel/config/device-tree/overlays/

Adding custom DT overlays

It is possible to add custom overlay/s via a bbappend recipe.

recipies-bsp
     - sunxi-overlays
        - sunxi-overlays%.bbappend
        - files
            - <custom.dts>

Inside the .bbappend the following metadata is requried:

FILESEXTRAPATHS:prepend := "${THISDIR}/files:" SRC_URI:${SOC_FAMILY}:append = " file://<custom.dts>"


Don't forget to add the custom overlay in your image or local configuration:

SUNXI_OVERLAYS_ENABLED:append = " "