ROCKPro64 Device Tree Overlays on Mainline - Revision history

CounterPillow at 15:00, 29 December 2021

2021-12-29T15:00:22Z

← Older revision		Revision as of 15:00, 29 December 2021
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	If your u-boot has been compiled with <code>CONFIG_OF_LIBFDT_OVERLAY</code> (which Manjaro's ~~will be very soon~~), adding device tree overlays the mainline way is very simple and easy.		If your u-boot has been compiled with <code>CONFIG_OF_LIBFDT_OVERLAY</code> (which Manjaro's is), adding device tree overlays the mainline way is very simple and easy.

	== Writing Your Device Tree Overlay ==		== Writing Your Device Tree Overlay ==

CounterPillow: CounterPillow moved page ROCKPro64 Device Tree Overlays on Manjaro to ROCKPro64 Device Tree Overlays on Mainline: This is more generically applicable

2021-12-10T11:51:19Z

CounterPillow moved page ROCKPro64 Device Tree Overlays on Manjaro to ROCKPro64 Device Tree Overlays on Mainline: This is more generically applicable

← Older revision

Revision as of 11:51, 10 December 2021

CounterPillow: /* Further Reading */ add my repo to the further reading list

2021-12-09T18:02:00Z

Further Reading: add my repo to the further reading list

← Older revision		Revision as of 18:02, 9 December 2021
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	* [https://www.kernel.org/doc/html/latest/devicetree/overlay-notes.html Linux Kernel Documentation - Devicetree Overlay Notes]		* [https://www.kernel.org/doc/html/latest/devicetree/overlay-notes.html Linux Kernel Documentation - Devicetree Overlay Notes]
	* [https://elinux.org/Device_Tree_Usage Embedded Linux Wiki - Device Tree Usage]		* [https://elinux.org/Device_Tree_Usage Embedded Linux Wiki - Device Tree Usage]
			* [https://github.com/CounterPillow/overlay-examples CounterPillow's overlay-examples repository]

	[[Category:ROCKPro64]] [[Category:Guide]]		[[Category:ROCKPro64]] [[Category:Guide]]

CounterPillow: /* Loading It */

2021-12-08T16:39:42Z

Loading It

← Older revision		Revision as of 16:39, 8 December 2021
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	'''FDTOVERLAYS /dtbs/overlays/pcf8574.dtbo'''		'''FDTOVERLAYS /dtbs/overlays/pcf8574.dtbo'''
	APPEND initrd=/initramfs-linux.img console=ttyS2,1500000 root=LABEL=ROOT_MNJRO rw rootwait quiet splash plymouth.ignore-serial-consoles		APPEND initrd=/initramfs-linux.img console=ttyS2,1500000 root=LABEL=ROOT_MNJRO rw rootwait quiet splash plymouth.ignore-serial-consoles

			To specify multiple overlays, simply separate them with space on the same line.

	Now after a reboot, the device tree overlay file should be applied, and your kernel will see the new device. You can confirm this by dumping the device tree the kernel uses, and grepping it for whatever you added:		Now after a reboot, the device tree overlay file should be applied, and your kernel will see the new device. You can confirm this by dumping the device tree the kernel uses, and grepping it for whatever you added:

CounterPillow: Created page with "If your u-boot has been compiled with `CONFIG_OF_LIBFDT_OVERLAY` (which Manjaro's will be very soon), adding device tree overlays the mainline way is very simple an..."

2021-12-08T16:04:29Z

Created page with "If your u-boot has been compiled with <code>CONFIG_OF_LIBFDT_OVERLAY</code> (which Manjaro's will be very soon), adding device tree overlays the mainline way is very simple an..."

New page

If your u-boot has been compiled with <code>CONFIG_OF_LIBFDT_OVERLAY</code> (which Manjaro's will be very soon), adding device tree overlays the mainline way is very simple and easy.

== Writing Your Device Tree Overlay ==

First off, you'll have to write a device tree overlay. In this example, we'll enable the ROCKPro64's I2C bus that's exposed to the pin headers, and declare that a PCF8574 GPIO extender is hanging off it.

/dts-v1/;
/plugin/;

&i2c8 {
status = "okay";
#address-cells = <1>;
#size-cells = <0>;

pcf8574: pcf8574@20 {
compatible = "nxp,pcf8574";
reg = <0x20>;
gpio-controller;
#gpio-cells = <2>;
};
};

We'll go through this file line by line.

* <code>/dts-v1/;</code> specifies that this file is a DTS file.
* <code>/plugin/;</code> specifies that this is not just a regular device tree source file, but an overlay.
* <code>&i2c8 {</code> references the <code>i2c8</code> node in the device tree we're applying on top of, meaning we're going to modify this specific part of it.
* <code>status = "okay";</code> enables the <code>i2c8</code> node. It's set to "disabled" in the tree we're applying on top of, specifying the property like this overrides it.
* <code>#address-cells = <1>;</code> is already set in the base tree, but since the compiler doesn't know what the base tree is, it'll yell at us if we don't set this.
* <code>#size-cells = <0>;</code> same as above.
* <code>pcf8574: pcf8574@20 {</code> adds a child node labelled <code>pcf8574</code> to the i2c8 node, which is a PCF8574 controller at address <tt>0x20</tt>.
* <code>compatible = "nxp,pcf8574";</code> the compatible string of the node, letting the kernel know what driver it needs to load for it.
* <code>reg = <0x20>;</code> the I2C address the device is listening on, in hexadecimal.
* <code>gpio-controller;</code> declares that this node is a GPIO controller.
* <code>#gpio-cells = <2>;</code> required for GPIO controllers.

Assuming we've saved this as <tt>pcf8574.dts</tt>, we can compile it as follows:

dtc -O dtb -o pcf8574.dtbo -@ pcf8574.dts

This creates a compiled <tt>pcf8574.dtbo</tt> from the <tt>pcf8574.dts</tt> input file, and with <code>-@</code> we preserve the labels of nodes, which in turn allows something to more easily overlay onto this overlay.

== Loading It ==

Next, copy your compiled device tree overlay file—in the previous example <tt>pcf8574.dtbo</tt>—somewhere into your <tt>/boot</tt>, for example <tt>/boot/dtbs/overlays/</tt>.

Then we modify <tt>/boot/extlinux/extlinux.conf</tt> and add the line emphasised in bold to it:

LABEL Manjaro ARM
KERNEL /Image
FDT /dtbs/rockchip/rk3399-rockpro64.dtb
'''FDTOVERLAYS /dtbs/overlays/pcf8574.dtbo'''
APPEND initrd=/initramfs-linux.img console=ttyS2,1500000 root=LABEL=ROOT_MNJRO rw rootwait quiet splash plymouth.ignore-serial-consoles

Now after a reboot, the device tree overlay file should be applied, and your kernel will see the new device. You can confirm this by dumping the device tree the kernel uses, and grepping it for whatever you added:

dtc -I fs /sys/firmware/devicetree/base | grep -A4 'pcf8574'

== Further Reading ==

* [https://www.kernel.org/doc/html/latest/devicetree/overlay-notes.html Linux Kernel Documentation - Devicetree Overlay Notes]
* [https://elinux.org/Device_Tree_Usage Embedded Linux Wiki - Device Tree Usage]

[[Category:ROCKPro64]] [[Category:Guide]]

ROCKPro64 Device Tree Overlays on Mainline - Revision history

CounterPillow at 15:00, 29 December 2021

CounterPillow: CounterPillow moved page ROCKPro64 Device Tree Overlays on Manjaro to ROCKPro64 Device Tree Overlays on Mainline: This is more generically applicable

CounterPillow: /* Further Reading */ add my repo to the further reading list

CounterPillow: /* Loading It */

CounterPillow: Created page with "If your u-boot has been compiled with CONFIG_OF_LIBFDT_OVERLAY (which Manjaro's will be very soon), adding device tree overlays the mainline way is very simple an..."

CounterPillow: Created page with "If your u-boot has been compiled with `CONFIG_OF_LIBFDT_OVERLAY` (which Manjaro's will be very soon), adding device tree overlays the mainline way is very simple an..."