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Stefan Wahren edited this page Aug 13, 2016 · 57 revisions

Recently there has been a focused effort to lay the ground work for a future switch from ARCH_BCM2708 to ARCH_BCM2835. This document has been updated to reflect the current status of using ARCH_BCM2835 downstream.

The official Raspberry Pi kernels support dual booting with Device Tree and with ATAGS. The bootloader inspects the kernel image for a trailing tag to determine if it should boot with Device Tree (mkknlimg). This can be overridden in /boot/config.txt.
So a switch to ARCH_BCM2835 necessitates dropping ATAGS support (no roadmap is known).

From 4.2 ARCH_BCM2835 should be functionally equivalent to ARCH_BCM2708.

Another status page: http://elinux.org/RPi_Upstreaming

VideoCore bootloader

The boot loader can boot ARCH_BCM2835 directly. The kernel has to be tagged with the mkknlimg utility.

Default configs

For Raspberry Pi 1, use bcm2835_defconfig

For Raspberry Pi 2, use multi_v7_defconfig

For Raspberry Pi 3, use defconfig on arm64. Note that as of 4.8-rc1, the defconfig has not been updated to include Raspberry Pi support, so you'll need to include:

CONFIG_ARCH_BCM2835
CONFIG_SERIAL_8250_BCM2835AUX
CONFIG_I2C_BCM2835
CONFIG_BCM2835_WDT
CONFIG_SPI_BCM2835
CONFIG_SPI_BCM2835AUX
CONFIG_DRM_VC4
CONFIG_SND_BCM2835_SOC_I2S
CONFIG_USB_DWC2_HOST
CONFIG_DMA_BCM2835
CONFIG_BCM2835_MBOX
CONFIG_RASPBERRYPI_POWER
CONFIG_RASPBERRYPI_FIRMWARE

DMA Engine

Mainline: bcm2835-dma
Downstream: bcm2708_dma

bcm2708-dmaengine has to be used for 2 reasons:

Mailbox

Mainline: bcm2835-mailbox

Firmware

Acked patch: dt/bindings: Add binding for the Raspberry Pi firmware driver
Downstream: raspberrypi-firmware

Provides an API to access the mailbox property channel.

This driver has a downstream patch to turn on USB power.

Thermal

Downstream: bcm2835_thermal

Depends on the firmware API.

CPU Frequency

Downstream: bcm2835-cpufreq

Depends on the firmware API.

Touchscreen driver for pi LCD display

Downstream: rpi-ft5406

Depends on the firmware API.

MMC

Mainline: sdhci-iproc
Downstream: bcm2835-mmc

bcm2835-mmc has increased throughput.

Framebuffer

Mainline: simplefb
Downstream: bcm2708_fb

Depends on the firmware API.

VCHIQ

Downstream: vchiq

Kernel to VideoCore communication interface.
Depends on the firmware API.

Onboard audio

Downstream: sound/arm/bcm2835.c

Depends on vchiq.

USB controller

Mainline: dwc2
Downstream: dwc_otg

The downstream driver uses FIQ resulting in increased performance.

GPIO LIRC

Downstream: lirc_rpi

Homebrew GPIO Port Receiver/Transmitter for the RaspberryPi

Videocore Memory

Downstream: vc-mem

Helper for videocore memory access and total size allocation.

Example:

$ sudo vcdbg log msg 2>&1 | grep Loading
000913.584: Loading 'kernel.img' from SD card

Videocore CMA

Downstream: vc_cma

Helper for videocore CMA access.

VMCS Shared Memory

Downstream: vc-sm

Support for the VC shared memory on the Broadcom reference design. Uses the VCHIQ stack.

Poweroff

Currently poweroff/halt leads to reboot.

The restart/poweroff code is being moved to the watchdog driver (linux-next): ARM: bcm2835: Move the restart/power_off handling to the WDT driver

This acked patch fixes the poweroff problem: [PATCH v3] watchdog: bcm2835: Fix poweroff behaviour

Revision & Serial numbers

Downstream commit: ARM: bcm2835: Set Serial number and Revision

Several Pi specific applications depend on the Revision and Serial numbers in /proc/cpuinfo:

$ cat /proc/cpuinfo
Revision        : 000e
Serial          : 000000004939788f

GPIO

Mainline: pinctrl-bcm2835

Downstream patches:

SPI

Mainline: spi-bcm2835

I2C

Mainline: i2c-bcm2835

I2S

Mainline: bcm2835-i2s

Various downstream audio cards: https://github.com/raspberrypi/linux/tree/rpi-4.2.y/sound/soc/bcm

PWM

Mainline: pwm-bcm2835

Want to contribute to our Linux kernel?

Fork this repo, make your changes, then send us a pull request

One caveat. If you are making changes to upstream code (i.e. with no changes specific to Raspberry Pi devices), then it's best to submit your changes upstream, then when they are accepted, we can cherry-pick them back to our branches here.

Clone this wiki locally