The document describes the Device Tree format used on ARM systems to describe hardware configurations to the Linux kernel. It defines the Device Tree in files with a .dts extension that are compiled to a binary .dtb blob. The Tree defines hardware using a tree of nodes and properties. It allows the kernel to be hardware-agnostic by obtaining configuration from the Device Tree rather than being compiled with board-specific code.

1. 11 Avenue Marigny 13014 Marseille www.ciose.fr christian.charreyre@ciose.fr
Le Device Tree Linux 127/06/17
Le Device Tree Linux

2. Le Device Tree Linux 227/06/17
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3. Présentation de CIO Systèmes
Embarqués
 Bureau d’études de 15 personnes
 Ingénierie électronique et informatique
 Expertise Linux embarqué depuis 15 ans
 Open Embedded et Yocto depuis 7 ans
 Siège à Saint-Etienne
 Capital de 60 000€
 Agence à Marseille
 Agréé CIR (Crédit d’Impôt Recherches)
 Expert programme Cap’tronic sur Linux embarqué
Le Device Tree Linux 327/06/17

4. Le Device Tree Linux
Présentation de l’orateur
4
 Associé au sein de CIO
 Responsable des technologies Linux embarqué
 Formateur Linux embarqué (avec Captronic et en direct)
 30 ans dans l'embarqué et le monde Unix / Linux
 Fervent promoteur du logiciel libre
 Membre de Medinsoft – Commission Logiciel Libre
27/06/17

5. Le Device Tree Linux 527/06/17
Architecture ARM dans le kernel
● “Gah. Guys, this whole ARM thing is a f*cking pain in the
ass”
Linus Torvalds à propos du support ARM dans le kernel

6. Le Device Tree Linux 627/06/17
Architecture ARM dans le kernel
X86 dans le kernel 3.0.35

7. Le Device Tree Linux 727/06/17
Architecture ARM dans le kernel
ARM dans le kernel 3.0.35

8. Le Device Tree Linux 827/06/17
Architecture ARM dans le kernel
● Le monde ARM, c’est :
– Nombreux fondeurs
– Nombreux SOC
● Dans le kernel ARM plusieurs étages de spécialisation :
– Platform
– Mach
– Board

9. Le Device Tree Linux 927/06/17
Architecture ARM dans le kernel
● Beaucoup de duplication de code, en particulier pour tout ce qui
n’est pas plug and play (platform_data)
static const struct esdhc_platform_data mx6q_hera_sd3_data
__initconst = {
.cd_gpio = HERA_SD3_CD,
.wp_gpio = HERA_SD3_WP,
.keep_power_at_suspend = 1,
.support_8bit = 0,
.delay_line = 0,
.cd_type = ESDHC_CD_CONTROLLER,
};

10. Le Device Tree Linux 1027/06/17
Pourquoi le Device Tree ?
● Idée :
– mutualiser le code kernel ARM
– tendre vers un kernel générique qui exploite une description du
hardware
● Implémentation dérivée du concept OpenFirmware de IEEE
● Décrire le matériel non plug and play dans une structure de données
● Le kernel généricisé exploite cette structure de données
– le bootloader charge et transmet cette structure au kernel (idem initial
ram disk)
● Le bootloader lui même peut éventuellement exploiter cette structure

11. Le Device Tree Linux 1127/06/17
Définir son Device Tree
●
Définition dans des fichiers texte (dts et dtsi) sous forme d’arbre
●
Selon une syntaxe normée à base de nœuds et propriétés
●
Éléments de syntaxe décrits dans la documentation kernel :
Documentation/devicetree/bindings
●
Constitue un éléments de l’API kernel  stabilité nécessaire des bindings
● Exemple : correspondance avec la structure platform_data précédente :
&usdhc4 {
pinctrl­names = "default";
pinctrl­0 = <&pinctrl_usdhc4>;
bus­width = <8>;
non­removable;
keep­power­in­suspend;
status = "okay";
};

12. Le Device Tree Linux 1227/06/17
Définir son Device Tree
● Le Device Tree (.dts) est compilé avec dtc pour générer un
fichier de données binaire .dtb (blob)
● C’est le dtb qui est exploité par le kernel

13. Le Device Tree Linux 1327/06/17
Définir son Device Tree - Exemple
/{
compatible = "nvidia,harmony", "nvidia,tegra20";
#address-cells = <1>;
#size-cells = <1>;
interrupt-parent = <&intc>;
chosen { };
aliases { };
memory {
device_type = "memory";
reg = <0x00000000 0x40000000>;
};
soc {
compatible = "nvidia,tegra20-soc", "simple-bus";
#address-cells = <1>;
#size-cells = <1>;
ranges;
intc: interrupt-controller@50041000 {
compatible = "nvidia,tegra20-gic";
interrupt-controller;
#interrupt-cells = <1>;
reg = <0x50041000 0x1000>, < 0x50040100 0x0100 >;
};
serial@70006300 {
compatible = "nvidia,tegra20-uart";
reg = <0x70006300 0x100>;
interrupts = <122>;
};
i2s1: i2s@70002800 {
compatible = "nvidia,tegra20-i2s";
reg = <0x70002800 0x100>;
interrupts = <77>;
codec = <&wm8903>;
};
i2c@7000c000 {
compatible = "nvidia,tegra20-i2c";
#address-cells = <1>;
#size-cells = <0>;
reg = <0x7000c000 0x100>;
Interrupts = <70>;
wm8903: codec@1a {
compatible = "wlf,wm8903";
reg = <0x1a>;
interrupts = <347>;
};
};
};
Nœud
Nœud
Propriété

14. Le Device Tree Linux 1427/06/17
Définir son Device Tree - Inclusions
imx6q-hera.dts
/*
* Copyright 2015 CIO Systèmes Embarqués.
* Copyright 2012 Freescale Semiconductor, Inc.
* Copyright 2011 Linaro Ltd.
*
* The code contained herein is licensed under the GNU General Public
* License. You may obtain a copy of the GNU General Public License
* Version 2 or later at the following locations:
*
* http://www.opensource.org/licenses/gpl-license.html
* http://www.gnu.org/copyleft/gpl.html
*/
/dts-v1/;
#include "imx6q.dtsi"
#include "imx6qdl-hera.dtsi"
…
&ldb {
lvds-channel@0 {
crtc = "ipu2-di0";
};
lvds-channel@1 {
crtc = "ipu2-di1";
};
};
...
imx6q.dtsi
...
#include <dt-bindings/interrupt-controller/irq.h>
#include "imx6q-pinfunc.h"
#include "imx6qdl.dtsi"
...
imx6qdl.dtsi
…
ldb: ldb@020e0008 {
#address-cells = <1>;
#size-cells = <0>;
gpr = <&gpr>;
status = "disabled";
lvds-channel@0 {
#address-cells = <1>;
#size-cells = <0>;
reg = <0>;
status = "disabled";
};
lvds-channel@1 {
#address-cells = <1>;
#size-cells = <0>;
reg = <1>;
status = "disabled";
};
};
…
Modification
définition nœud
ldb@020e0008
Étiquette

15. Le Device Tree Linux 1527/06/17
Device Tree - Inclusions
● Les inclusions multiples permettent d’aller du plus général
au plus particulier, sans duplication
● Modification ou enrichissement de nœuds à l’aide des
étiquettes
imx6qdl.dtsi
imx6q.dtsi imx6dl.dtsi
imx6q-
sabresd.dts
imx6q-
sabreauto.dts
imx6q-
hera.dts
imx6dl-
sabrelite.dts
imx6dl-
sabreauto.dts
imx6dl-
udoo.dts
SOCs
Cartes

16. Le Device Tree Linux 1627/06/17
Définir son Device Tree - Inclusions
imx6q-hera.dts
…
&i2c3 {
ov5640_mipi: ov5640_mipi@3c { /* mipi camera */
compatible = "ovti,ov5640_mipi";
reg = <0x3c>;
clocks = <&clks 201>;
clock-names = "csi_mclk";
pwn-gpios = <&gpio2 3 1>; /* active low: SD1_CLK */
rst-gpios = <&gpio2 2 0>; /* active high: SD1_DAT2 */
csi_id = <1>;
mclk = <24000000>;
mclk_source = <0>;
status = "disabled";
};
};
...
imx6qdl.dtsi
…
gpio1: gpio@0209c000 {
compatible = "fsl,imx6q-gpio", "fsl,imx35-gpio";
reg = <0x0209c000 0x4000>;
interrupts = <0 66 IRQ_TYPE_LEVEL_HIGH>,
<0 67 IRQ_TYPE_LEVEL_HIGH>;
gpio-controller;
#gpio-cells = <2>;
interrupt-controller;
#interrupt-cells = <2>;
};
gpio2: gpio@020a0000 {
compatible = "fsl,imx6q-gpio", "fsl,imx35-gpio";
reg = <0x020a0000 0x4000>;
interrupts = <0 68 IRQ_TYPE_LEVEL_HIGH>,
<0 69 IRQ_TYPE_LEVEL_HIGH>;
gpio-controller;
#gpio-cells = <2>;
interrupt-controller;
#interrupt-cells = <2>;
};
…
Phandle =
référence vers
autre nœud Étiquette

17. Le Device Tree Linux 1727/06/17
Lien Device Tree - Kernel
● Le lien se fait à l’aide de la propriété compatible
regulator-1p1@110 {
compatible = "fsl,anatop-regulator";
regulator-name = "vdd1p1";
regulator-min-microvolt = <800000>;
regulator-max-microvolt = <1375000>;
regulator-always-on;
anatop-reg-offset = <0x110>;
anatop-vol-bit-shift = <8>;
anatop-vol-bit-width = <5>;
anatop-min-bit-val = <4>;
anatop-min-voltage = <800000>;
anatop-max-voltage = <1375000>;
anatop-enable-bit = <0>;
};

18. Le Device Tree Linux 1827/06/17
Lien Device Tree - Kernel
drivers/regulator/anatop-regulator.c
…
static const struct of_device_id of_anatop_regulator_match_tbl[] = {
{ .compatible = "fsl,anatop-regulator", },
{ /* end */ }
};
static struct platform_driver anatop_regulator_driver = {
.driver = {
.name = "anatop_regulator",
.of_match_table = of_anatop_regulator_match_tbl,
},
.probe = anatop_regulator_probe,
};
static int __init anatop_regulator_init(void)
{
return platform_driver_register(&anatop_regulator_driver);
}
postcore_initcall(anatop_regulator_init);
static void __exit anatop_regulator_exit(void)
{
platform_driver_unregister(&anatop_regulator_driver);
}
module_exit(anatop_regulator_exit);
...
drivers/regulator/anatop-regulator.c
…
static int anatop_regulator_probe(struct platform_device *pdev)
{
…
sreg->name = of_get_property(np, "regulator-name", NULL);
if (!sreg->name) {
dev_err(dev, "no regulator-name setn");
return -EINVAL;
}
...
ret = of_property_read_u32(np, "anatop-min-voltage",
&sreg->min_voltage);
if (ret) {
dev_err(dev, "no anatop-min-voltage property setn");
return ret;
}
ret = of_property_read_u32(np, "anatop-max-voltage",
&sreg->max_voltage);
if (ret) {
dev_err(dev, "no anatop-max-voltage property setn");
return ret;
}
...

19. Le Device Tree Linux 1927/06/17
Un exemple : bus ecspi1 de la
carte Hera
AIP
S

20. Le Device Tree Linux 2027/06/17
Un exemple : bus ecspi1 de la
carte Hera
Documentation/devicetree/bindings/spi/fsl-imx-cspi.txt
* Freescale (Enhanced) Configurable Serial Peripheral Interface
(CSPI/eCSPI) for i.MX
Required properties:
- compatible :
- "fsl,imx1-cspi" for SPI compatible with the one integrated on i.MX1
- "fsl,imx21-cspi" for SPI compatible with the one integrated on i.MX21
- "fsl,imx27-cspi" for SPI compatible with the one integrated on i.MX27
- "fsl,imx31-cspi" for SPI compatible with the one integrated on i.MX31
- "fsl,imx35-cspi" for SPI compatible with the one integrated on i.MX35
- "fsl,imx51-ecspi" for SPI compatible with the one integrated on i.MX51
- reg : Offset and length of the register set for the device
- interrupts : Should contain CSPI/eCSPI interrupt
- fsl,spi-num-chipselects : Contains the number of the chipselect
- cs-gpios : Specifies the gpio pins to be used for chipselects.
- clocks : Clock specifiers for both ipg and per clocks.
- clock-names : Clock names should include both "ipg" and "per"
See the clock consumer binding,
Documentation/devicetree/bindings/clock/clock-bindings.txt
- dmas: DMA specifiers for tx and rx dma. See the DMA client binding,
Documentation/devicetree/bindings/dma/dma.txt
- dma-names: DMA request names should include "tx" and "rx" if present.
Documentation/devicetree/bindings/spi/fsl-imx-cspi.txt
Example:
ecspi@70010000 {
#address-cells = <1>;
#size-cells = <0>;
compatible = "fsl,imx51-ecspi";
reg = <0x70010000 0x4000>;
interrupts = <36>;
fsl,spi-num-chipselects = <2>;
cs-gpios = <&gpio3 24 0>, /* GPIO3_24 */
<&gpio3 25 0>; /* GPIO3_25 */
dmas = <&sdma 3 7 1>, <&sdma 4 7 2>;
dma-names = "rx", "tx";
};
#address-cells = nombre mots de
32 bits dans l’adresse de reg pour
les nœuds sur le bus
#size-cells = nombre mots de
32 bits dans la taille de reg pour
les nœuds sur le bus
reg = @ et taille du contrôleur
dans le SOC

21. Le Device Tree Linux 2127/06/17
Un exemple : bus ecspi1 de la
carte Hera
imx6qdl.dtsi
soc {
#address-cells = <1>;
#size-cells = <1>;
compatible = "simple-bus";
interrupt-parent = <&gpc>;
ranges;
….
aips-bus@02000000 { /* AIPS1 */
compatible = "fsl,aips-bus", "simple-bus";
#address-cells = <1>;
#size-cells = <1>;
reg = <0x02000000 0x100000>;
ranges;
spba-bus@02000000 {
compatible = "fsl,spba-bus", "simple-bus";
#address-cells = <1>;
#size-cells = <1>;
reg = <0x02000000 0x40000>;
ranges;
….
imx6qdl.dtsi
….
ecspi1: ecspi@02008000 {
#address-cells = <1>;
#size-cells = <0>;
compatible = "fsl,imx6q-ecspi", "fsl,imx51-ecspi";
reg = <0x02008000 0x4000>;
interrupts = <0 31 IRQ_TYPE_LEVEL_HIGH>;
clocks = <&clks IMX6QDL_CLK_ECSPI1>,
<&clks IMX6QDL_CLK_ECSPI1>;
clock-names = "ipg", "per";
dmas = <&sdma 3 7 1>, <&sdma 4 7 2>;
dma-names = "rx", "tx";
status = "disabled";
};
….
};
….
};
….
};
Inhibé par
défaut

22. Le Device Tree Linux 2227/06/17
Un exemple : bus ecspi1 de la
carte Hera
imx6qdl-hera.dtsi
&ecspi1 {
fsl,spi-num-chipselects = <2>;
cs-gpios = <&gpio4 9 0>, /* GPIO4_9 */
<&gpio4 10 0>; /* GPIO4_10 */
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_ecspi1>;
status = "okay";
};
imx6q-hera.dts
ti,x-plate-ohms = /bits/ 16 <180>;
ti,pressure-max = /bits/ 16 <255>;
ti,keep-vref-on;
linux,wakeup;
status = "enabled";
};
touchscreen_1: ads7845@1 { /*TS 5 wires on CS1: ADS7845 */
compatible = "ti,ads7845";
reg = <1>; /* CS1 */
spi-max-frequency = <3000000>;
interrupt-parent = <&gpio1>;
interrupts = <2 0>; /* TCH_INT1 */
pendown-gpio = <&gpio1 2 0>;
ti,vref-mv = /bits/ 16 <3300>;
ti,x-min = /bits/ 16 <0x0>;
ti,x-max = /bits/ 16 <0x0fff>;
ti,y-min = /bits/ 16 <0x0>;
ti,y-max = /bits/ 16 <0x0fff>;
ti,x-plate-ohms = /bits/ 16 <180>;
ti,pressure-max = /bits/ 16 <255>;
ti,keep-vref-on;
linux,wakeup;
status = "disabled";
};
};
Activation
+
définition
propriétés
imx6q-hera.dts
&ecspi1 {
touchscreen_0: ads7845@0 { /*TS 4 wires on CS0: TSC2008
SPI communication OK but no value transmited to ts_lib*/
compatible = "ti,ads7846";
reg = <0>; /* CS0 */
spi-max-frequency = <3000000>;
interrupt-parent = <&gpio1>;
interrupts = <0 0>; /* TCH_INT0 */
pendown-gpio = <&gpio1 0 0>;
ti,vref-mv = /bits/ 16 <3300>;
ti,x-min = /bits/ 16 <0x0>;
ti,x-max = /bits/ 16 <0x0fff>;
ti,y-min = /bits/ 16 <0x0>;
ti,y-max = /bits/ 16 <0x0fff>;
ecspi1: ecspi@02008000 {
#address-cells =
<1>;
#size-cells =
<0>;

23. Le Device Tree Linux 2327/06/17
Appel à orateurs
● Recherche d’orateurs sur sujets ouverts pour prochain
meetup
● Me proposer un thème par email
christian.charreyre@ciose.fr
● Éventuellement on peut envisager plusieurs mini
présentations