U-Boot APIs

FDT Interfaces

The Flattened Device Tree (FDT) interfaces are used to include part of the device information structure in the device tree file.

Table 1. **fdt_getprop**
Synopsis	`const void fdt_getprop(const void fdt, int nodeoffset, const char name, int lenp)`
Description	Retrieves the value of a given property.
Parameter	fdt: The pointer to the DTB file nodeoffset: The offset of the node to get property from name: The name of the property lenp: The pointer to an integer variable (will be overwritten) or NULL
Return	Success: The pointer to the property's value. If lenp is not NULL, lenp will contain the length of the property value (>= 0). Failure: NULL.If lenp* is not NULL, *lenp will contain an error code (< 0): FDT_ERR_NOTFOUND: The target property is not found. FDT_ERR_BADOFFSET: The node offset is invalid. The node offset does not point to the FDT_BEGIN_NODE tag. FDT_ERR_BADMAGIC: The magic field is invalid. FDT_ERR_BADVERSION: The version is invalid. FDT_ERR_BADSTATE: The state is invalid. FDT_ERR_BADSTRUCTURE: The file structure is invalid. FDT_ERR_TRUNCATED, standard meanings.

Table 2. fdt_set_node_status
Synopsis	`int fdt_set_node_status(void *fdt, int nodeoffset, enum fdt_status sta-tus, unsigned int error_code)`
Description	Sets the status of a node.
Parameter	fdt: The pointer to the DTB file. status: The following statuses are available. FDT_STATUS_OKAY - FDT_STATUS_DISABLED - FDT_STATUS_FAIL - FDT_STATUS_FAIL_ERROR_CODE - error_code: optional, only used if status is FDT_STATUS_FAIL_ERROR_CODE
Return	Success: 0. Failure: Any value other than 0.

Table 3. fdt_path_offset
Synopsis	`int fdt_path_offset(const void fdt, const char path);`
Description	Finds a tree node by its full path.
Parameter	fdt: The pointer to the DTB file. path: The full path to the node. error_code: optional, only used if status is FDT_STATUS_FAIL_ERROR_CODE.
Return	Success: The structure block offset of the node with the requested path (>= 0). Failure: Any value < 0.

ENV Interfaces

The environment (ENV) interfaces are used to provide U-Boot with the capabilities of dynamic configuration during program operation. U-Boot defines a set of default environment variables in file include/env_default.h.

Table 4. int env_set
Synopsis	`int env_set(const char varname, const char value);`
Description	Sets an environment variable.
Parameter	varname: The environment variable you want to change. varvalue: The new value of the environment variable.
Return	Success: 0. Failure: 1.

Table 5. env_get
Synopsis	`char env_get(const char varname);`
Description	Gets the value of an environment variable.
Parameter	varname: The environment variable you want to get value from.
Return	Success: Value of the target environment variable, or "NULL" if the environment variable is not found. Failure: Any other values.

Table 6. env_set
Synopsis	`int env_save(void);`
Description	Saves the environment variables to storage.
Parameter	None
Return	Success: 0. Failure: Any value other than 0.

U-Boot Commands

The U-Boot command line interfaces are used to create a minimum valid command line interface. So, after you start up U-Boot, you can have access to a lot of command lines, including tftp, bootm, and booti.

Table 7. run_command_list
Synopsis	`int run_command_list(const char *cmd, int len, int flag)`
Description	Executes the U-Boot command line.
Parameter	cmd: The pointer to the command. len: The length of the command line. To load the length automatically, set this value to “`-1`”. flag: Not used.
Return	Success: 0. Failure: Any value other than 0.

Table 8. do_bootm
Synopsis	`int do_bootm(struct cmd_tbl cmdtp, int flag, int argc, char const argv[]);`
Description	Runs the `bootm` command, and boots the application from the image in memory.
Parameter	cmdtp: The command information for the `bootm` command flag: The command flags argc: The number of arguments agrv: The list of arguments
Return	Success: 0. Failure: Any value other than 0.

Table 9. do_booti
Synopsis	`int do_booti(struct cmd_tbl cmdtp, int flag, int argc, char const argv[]);`
Description	Runs the `booti` command, and boots the Linux kernel "Image" format from memory.
Parameter	cmdtp: The command information for the `booti` command flag: The command flags argc: The number of arguments agrv: The list of arguments
Return	Success: 0. Failure: Any value other than 0.

Table 10. do_tftpb
Synopsis	`int do_tftpb(struct cmd_tbl cmdtp, int flag, int argc, char const argv[]);`
Description	Runs the `tftpboot` command, and boots the image via network using TFTP protocol.
Parameter	cmdtp: The command information for the `tftpboot` command flag: The command flags argc: The number of arguments agrv: The list of arguments
Return	Success: 0. Failure: Any value other than 0.

Table 11. do_mmcinfo
Synopsis	`static int do_mmcinfo(struct cmd_tbl cmdtp, int flag, int argc, char const argv[])`
Description	Runs the `mmcinfo` command, and displays the information of the current MMC device.
Parameter	cmdtp: The command information for the `mmcinfo` command flag: The command flags argc: The number of arguments agrv: The list of arguments
Return	Success: 0. Failure: 1

Flash Read and Write

The flash read and write interfaces are used to read data from and write data to the SPI flash. This can be used to flash images to the SPI flash via serial interfaces under U-Boot mode.

Table 12. spi_flash_read
Synopsis	`static inline int spi_flash_read(struct spi_flash flash, u32 offset, size_t len, void buf)`
Description	Reads data from the SPI flash.
Parameter	flash: The SPI flash device offset: The address offset of the above device in bytes len: The length of bytes to read buf: The buffer to store the read data
Return	Success: 0. Failure: Any value other than 0

Table 13. spi_flash_write
Synopsis	`static inline int spi_flash_write(struct spi_flash flash, u32 offset, size_t len, const void buf)`
Description	Writes data into the SPI flash.
Parameter	flash: The SPI flash device offset: The address offset of the above device in bytes len: The length of bytes to write buf: The buffer to store the data to write
Return	Success: 0. Failure: Any value other than 0

Partition

The partition information interface is used to find a partition by partition name in all registered partitions and get its partition information.

Table 14. part_get_info_by_name
Synopsis	`int part_get_info_by_name(struct blk_desc dev_desc, const char name, struct disk_partition *info);`
Description	Finds a partition by partition name in all registered partitions and get its partition information.
Parameter	dev_desc: The device descriptor name: The name of the specific partition table entry info: The partition information to query
Return	Success: The target partition information Failure: -1.

GPIO Operations

The GPIO operation interfaces are used to get and set GPIO levels to read the input and output status and alter the GPIO from an output to an output.

Table 15. gpio_get_value
Synopsis	`int gpio_get_value(unsigned gpio)`
Description	Gets the level from a target GPIO interface. The level is used to define whether the GPIO is an input or an output.
Parameter	gpio: The GPIO index number
Return	Success: The level of the target GPIO interface: 0 as low level, 1 as high level Failure: -1.

Table 16. gpio_set_value
Synopsis	`void gpio_set_value(unsigned gpio, int value)`
Description	Sets the level to a target GPIO interface. The level can be used to alter the GPIO from an output to an output.
Parameter	gpio: The GPIO index number value: The expected level: 0 as low level, 1 as high level
Return	None