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