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Device Tree on ARCH_BCM2708
This page details the work getting Device Tree support on ARCH_BCM2708 (used in the official RPi kernel).
The work is done in parallel with the Upstreaming (ARCH_BCM2835) effort.
Moving to ARCH_BCM2835 can take some time, so this aims at giving Device Tree support sooner.
Core Device Tree support is added.
Devices that can be added: Platform, SPI and I2C
These drivers are needed to give full Device Tree support for the end user
| ARCH_BCM2708 | ARCH_BCM2835 | Status |
|---|---|---|
| bcm2708_gpio | pinctrl-bcm2835 | pinctrl-bcm2708 is added |
| spi-bcm2708 | spi-bcm2835 | OK |
| i2c-bcm2708 | i2c-bcm2835 | OK |
| ARCH_BCM2708 | ARCH_BCM2835 | Status |
|---|---|---|
| bcm2708_wdog | bcm2835_wdt | |
| bcm2708-rng | bcm2835-rng | |
| bcm2708-i2s | bcm2835-i2s |
Install kernel
sudo REPO_URI=https://github.com/notro/rpi-firmware BRANCH=dt rpi-update
[...]
*** Running post-install script
/lib/firmware
Backup /boot/config.txt -> /boot/config.txt.2014-07-30--15-43-04
Adding Device Tree options to /boot/config.txt
Remember to restore/edit /boot/config.txt when installing a non-DT kernel
[...]
Build dtc from source to get the ability to add properties to the dtb
sudo apt-get install flex bison
git clone http://git.jdl.com/software/dtc.git
cd dtc
make
# make install, puts the files in ~/, instead we do:
sudo cp -v libfdt/libfdt*.so /usr/lib/
sudo cp -v dtc fdtdump fdtget fdtput /usr/bin/
dtc -v
Version: DTC 1.4.0
Note: The debian pakage is too old:
sudo apt-get install device-tree-compiler
Setting up device-tree-compiler (1.3.0-4) ...
sudo fdtput -t s /boot/bcm2708-rpi-b.dtb /display status "disabled"
Error at 'status': FDT_ERR_NOSPACE
The status property determines whether the device is enabled or not.
Absent property, "okay" or "ok" value, means the device is enabled. Any other value means disabled.
Ref: http://lxr.free-electrons.com/ident?a=arm;i=__of_device_is_available
These files are used to build the bcm2708-rpi-b.dtb file
Enable SPI (also remove module blacklisting if on Raspian)
$ fdtget /boot/bcm2708-rpi-b.dtb /soc/spi@7e204000 status
disabled
$ sudo fdtput --type s /boot/bcm2708-rpi-b.dtb /soc/spi@7e204000 status "okay"
$ sudo reboot
Use the spi-bcm2835 driver
$ fdtget /boot/bcm2708-rpi-b.dtb /soc/spi@7e204000 compatible
brcm,bcm2708-spi
$ sudo fdtput --type s /boot/bcm2708-rpi-b.dtb /soc/spi@7e204000 compatible "brcm,bcm2835-spi"
$ fdtget /boot/bcm2708-rpi-b.dtb /soc/spi@7e204000 compatible
brcm,bcm2835-spi
$ sudo reboot
Note: This kernel doesn't have the ads7846 module. I have previously used this for testing in another kernel.
Get a device tree source representation
dtc -I dtb /boot/bcm2708-rpi-b.dtb > bcm2708-rpi-b.dts
Edit bcm2708-rpi-b.dts (also remove or disable spidev@1)
Add a label to the gpio node, so we can reference it
gpio: gpio {
Add node
spi@7e204000 {
tsc2046@1 {
compatible = "ti,tsc2046";
reg = <1>; /* CE1 */
interrupts = <3 17>; /* bank 3 is GPIO interrupts */
spi-max-frequency = <2000000>;
pendown-gpio = <&gpio 17 0>;
ti,x-min = /bits/ 16 <230>;
ti,x-max = /bits/ 16 <3850>;
ti,y-min = /bits/ 16 <190>;
ti,y-max = /bits/ 16 <3850>;
ti,x-plate-ohms = /bits/ 16 <60>;
ti,pressure-max = /bits/ 16 <255>;
linux,wakeup;
status = "okay";
};
};
Compile dts
dtc -I dts -O dtb -o bcm2708-rpi-b.dtb bcm2708-rpi-b.dts
Use it
sudo cp /boot/bcm2708-rpi-b.dtb /boot/bcm2708-rpi-b.dtb.backup
sudo cp bcm2708-rpi-b.dtb /boot/bcm2708-rpi-b.dtb
sudo reboot
Verify that the device is present
$ ls -l /proc/device-tree/soc/spi@7e204000/tsc2046@1/
total 0
-r--r--r-- 1 root root 11 Jul 30 16:20 compatible
-r--r--r-- 1 root root 8 Jul 30 16:20 interrupts
-r--r--r-- 1 root root 0 Jul 30 16:20 linux,wakeup
-r--r--r-- 1 root root 8 Jul 30 16:20 name
-r--r--r-- 1 root root 12 Jul 30 16:20 pendown-gpio
-r--r--r-- 1 root root 4 Jul 30 16:20 reg
-r--r--r-- 1 root root 4 Jul 30 16:20 spi-max-frequency
-r--r--r-- 1 root root 5 Jul 30 16:20 status
-r--r--r-- 1 root root 2 Jul 30 16:20 ti,pressure-max
-r--r--r-- 1 root root 2 Jul 30 16:20 ti,x-max
-r--r--r-- 1 root root 2 Jul 30 16:20 ti,x-min
-r--r--r-- 1 root root 2 Jul 30 16:20 ti,x-plate-ohms
-r--r--r-- 1 root root 2 Jul 30 16:20 ti,y-max
-r--r--r-- 1 root root 2 Jul 30 16:20 ti,y-min
$ cat /sys/devices/soc.0/20204000.spi/spi_master/spi0/spi0.1/modalias
spi:tsc2046
Enable i2c-1 (also remove module blacklisting if on Raspian)
$ fdtget /boot/bcm2708-rpi-b.dtb /soc/i2c@7e804000 status
disabled
$ sudo fdtput --type s /boot/bcm2708-rpi-b.dtb /soc/i2c@7e804000 status "okay"
$ sudo reboot
$ dmesg
[ 6.613730] bcm2708_i2c_init_pinmode(1,2)
[ 6.811634] bcm2708_i2c_init_pinmode(1,3)
[ 6.964823] bcm2708_i2c 20804000.i2c: BSC1 Controller at 0x20804000 (irq 79) (baudrate 100000)
[ 8.090310] pcm512x 1-004c: Failed to reset device: -5
[ 8.107153] pcm512x: probe of 1-004c failed with error -5
Use the i2c-bcm2835 driver
$ fdtget /boot/bcm2708-rpi-b.dtb /soc/i2c@7e804000 compatible
brcm,bcm2708-i2c
$ sudo fdtput --type s /boot/bcm2708-rpi-b.dtb /soc/i2c@7e804000 compatible "brcm,bcm2835-i2c"
$ fdtget /boot/bcm2708-rpi-b.dtb /soc/i2c@7e804000 compatible
brcm,bcm2835-i2c
$ sudo reboot
$ dmesg
[ 8.020037] i2c-bcm2835 20804000.i2c: i2c transfer failed: 100
[ 8.028457] pcm512x 1-004c: Failed to reset device: -121
[ 8.036192] pcm512x: probe of 1-004c failed with error -121
$ ls -l /dev/i2c*
crw-rw---T 1 root i2c 89, 1 Jul 28 20:47 /dev/i2c-1
The transfer error is related to the failed pcm512x probing.
Add to dts
i2c@7e804000 {
rtc@68 {
compatible = "dallas,ds1307";
reg = <0x68>;
};
};
Verify
$ dmesg
[ 6.895287] rtc-ds1307 1-0068: rtc core: registered ds1307 as rtc0
[ 6.903734] rtc-ds1307 1-0068: 56 bytes nvram
[ 7.242081] bcm2708_i2c 20804000.i2c: BSC1 Controller at 0x20804000 (irq 79) (baudrate 100000)
$ sudo hwclock -r
Mon 28 Jul 2014 20:26:15 UTC -0.905546 seconds
This kernel has DYNAMIC_DEBUG enabled.
https://www.kernel.org/doc/Documentation/dynamic-debug-howto.txt
sudo mount -t debugfs none /sys/kernel/debug/
sudo chmod 777 /sys/kernel/debug/
grep pinctrl /sys/kernel/debug/dynamic_debug/control
...
Adding this to /boot/cmdline.txt, gives some Device Tree related debug output:
debug dyndbg="module pinctrl_bcm2708 +p; file drivers/gpio/gpiolib.c +p; file drivers/of/platform.c +p; file kernel/irq/irqdomain.c +p; file kernel/irq/manage.c +p; file kernel/resource.c +p;"
How to build: http://elinux.org/RPi_Kernel_Compilation
Enable Device Tree
ARCH=arm make bcmrpi_defconfig
ARCH=arm make menuconfig
# System Type ---> Broadcom BCM2708 Implementations ---> [*] BCM2708 Device Tree support
The quick way including debug option
ARCH=arm make bcmrpi_defconfig
scripts/config --enable BCM2708_DT
# Device Tree contents in /proc/device-tree/
scripts/config --enable PROC_DEVICETREE
yes "" | ARCH=arm make oldconfig
Add to /boot/config.txt
device_tree=bcm2708-rpi-b.dtb
device_tree_address=0x100
kernel_address=0x8000
disable_commandline_tags=2
- Migrate to the Common Clock Framework
- BCM2708: Add core Device Tree support
- pinctrl: add bcm2708 driver
- spi: bcm2708: add device tree support
- i2c: bcm2708: add device tree support
- DT - Device Tree
- FDT - Flattended Device Tree: a DT representation used in the dtb blob.
- .dtb - Device Tree Binary
- .dts - Device Tree Source
- .dtsi - Device Tree Source Include
- dtc - Device Tree Compiler