The chosen node
---------------
The chosen node does not represent a real device, but serves as a place
for passing data like which serial device to used to print the logs etc
stdout-path property
--------------------
Device trees may specify the device to be used for boot console output
with a stdout-path property under /chosen.
Example
-------
/ {
chosen {
stdout-path = "/serial@f00:115200";
};
serial@f00 {
compatible = "vendor,some-uart";
reg = <0xf00 0x10>;
};
};
tick-timer property
-------------------
In a system there are multiple timers, specify which timer to be used
as the tick-timer. Earlier it was hardcoded in the timer driver now
since device tree has all the timer nodes. Specify which timer to be
used as tick timer.
Example
-------
/ {
chosen {
tick-timer = "/timer2@f00";
};
timer2@f00 {
compatible = "vendor,some-timer";
reg = <0xf00 0x10>;
};
};
u-boot,bootcount-device property
--------------------------------
In a DM-based system, the bootcount may be stored in a device known to
the DM framework (e.g. in a battery-backed SRAM area within a RTC
device) managed by a device conforming to UCLASS_BOOTCOUNT. If
multiple such devices are present in a system concurrently, then the
u-boot,bootcount-device property can select the preferred target.
Example
-------
/ {
chosen {
u-boot,bootcount-device = &bootcount-rv3029;
};
bootcount-rv3029: bootcount@0 {
compatible = "u-boot,bootcount-rtc";
rtc = &rv3029;
offset = <0x38>;
};
i2c2 {
rv3029: rtc@56 {
compatible = "mc,rv3029";
reg = <0x56>;
};
};
};
u-boot,spl-boot-order property
------------------------------
In a system using an SPL stage and having multiple boot sources
(e.g. SPI NOR flash, on-board eMMC and a removable SD-card), the boot
device may be probed by reading the image and verifying an image
signature.
If the SPL is configured through the device-tree, the boot-order can
be configured with the spl-boot-order property under the /chosen node.
Each list element of the property should specify a device to be probed
in the order they are listed: references (i.e. implicit paths), a full
path or an alias is expected for each entry.
A special specifier "same-as-spl" can be used at any position in the
boot-order to direct U-Boot to insert the device the SPL was booted
from there. Whether this is indeed inserted or silently ignored (if
it is not supported on any given SoC/board or if the boot-device is
not available to continue booting from) is implementation-defined.
Note that if "same-as-spl" expands to an actual node for a given
board, the corresponding node may appear multiple times in the
boot-order (as there currently exists no mechanism to suppress
duplicates from the list).
Example
-------
/ {
chosen {
u-boot,spl-boot-order = "same-as-spl", &sdmmc, "/sdhci@fe330000";
};
};
u-boot,spl-boot-device property
-------------------------------
This property is a companion-property to the u-boot,spl-boot-order and
will be injected automatically by the SPL stage to notify a later stage
of where said later stage was booted from.
You should not define this property yourself in the device-tree, as it
may be overwritten without warning.
firmware-loader property
------------------------
Multiple file system firmware loader nodes could be defined in device trees for
multiple storage type and their default partition, then a property
"firmware-loader" can be used to pass default firmware loader
node(default storage type) to the firmware loader driver.
Example
-------
/ {
chosen {
firmware-loader = &fs_loader0;
};
fs_loader0: fs-loader@0 {
bootph-all;
compatible = "u-boot,fs-loader";
phandlepart = <&mmc 1>;
};
};
u-boot,acpi-ssdt-order
----------------------
This provides the ordering to use when writing device data to the ACPI SSDT
(Secondary System Descriptor Table). Each cell is a phandle pointer to a device
node to add. The ACPI information is written in this order.
If the ordering does not include all nodes, an error is generated.
e820-entries
------------
This provides a way to add entries to the e820 table which tells the OS about
the memory map. The property contains three sets of 64-bit values:
address - Start address of region
size - Size of region
flags - Flags (E820_...)
Example:
chosen {
e820-entries = /bits/ 64 <
IOMAP_P2SB_BAR IOMAP P2SB_SIZE E820_RESERVED
MCH_BASE_ADDRESS MCH_SIZE E820_RESERVED>;
};