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Diffstat (limited to 'roms/u-boot/doc/device-tree-bindings/chosen.txt')
| -rw-r--r-- | roms/u-boot/doc/device-tree-bindings/chosen.txt | 163 |
1 files changed, 163 insertions, 0 deletions
diff --git a/roms/u-boot/doc/device-tree-bindings/chosen.txt b/roms/u-boot/doc/device-tree-bindings/chosen.txt new file mode 100644 index 000000000..e5ba6720c --- /dev/null +++ b/roms/u-boot/doc/device-tree-bindings/chosen.txt @@ -0,0 +1,163 @@ +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 { + u-boot,dm-pre-reloc; + 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>; +}; |