Access SPI bus in u-boot and Linux

Serial Peripheral Interface Bus - Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Serial_Peripheral_Interface_Bus

U-boot SPI test tool

The u-boot command sspi Usage:

sspi - SPI utility command
Usage:
sspi [<bus>:]<cs>[.<mode>] <bit_len> <dout> - Send and receive bits
<bus> - Identifies the SPI bus
<cs> - Identifies the chip select
<mode> - Identifies the SPI mode to use
<bit_len> - Number of bits to send (base 10)
<dout> - Hexadecimal string that gets sent
<dout> is in hex but without the prefix "0x". All others are in decimal.

The following is SPI mode defined in u-boot/include/spi.h. But still depends on the mode that SPI controller/driver can handle:

/* SPI mode flags */
#define SPI_CPHA        0x01                    /* clock phase */
#define SPI_CPOL        0x02                    /* clock polarity */
#define SPI_MODE_0      (0|0)                   /* (original MicroWire) */
#define SPI_MODE_1      (0|SPI_CPHA)
#define SPI_MODE_2      (SPI_CPOL|0)
#define SPI_MODE_3      (SPI_CPOL|SPI_CPHA)
#define SPI_CS_HIGH     0x04                    /* CS active high */
#define SPI_LSB_FIRST   0x08                    /* per-word bits-on-wire */
#define SPI_3WIRE       0x10                    /* SI/SO signals shared */
#define SPI_LOOP        0x20                    /* loopback mode */
#define SPI_SLAVE       0x40                    /* slave mode */
#define SPI_PREAMBLE    0x80                    /* Skip preamble bytes */

It depends on the requirement of the device, as well as the data sent to the device as command. Says we require bus=0, CS=2, data len=32, data=0x51525354, the device require SPI_3WIRE, SPI_CPHA, SPI_CPOL=> mode=0x13 (19).

# sspi 0:2.19 32 51525354
51525354

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Linux SPI test tool
Projet spi-tools « Christophe Blaess
http://www.blaess.fr/christophe/2014/08/12/projet-spi-tools/
https://github.com/cpb-/spi-tools

usage: ./spi-config options...
  options:
    -d --device=  use the given spi-dev character device.
    -q --query         print the current configuration.
    -m --mode=[0-3]    use the selected spi mode.
             0: low iddle level, sample on leading edge
             1: low iddle level, sample on trailing edge
             2: high iddle level, sample on leading edge
             3: high iddle level, sample on trailing edge
    -l --lsb={0,1}     LSB first (1) or MSB first (0)
    -b --bits=[7...]   bits per word
    -s --speed=   set the speed in Hz
    -h --help          this screen
    -v --version       display the version number

CPOL=1, idle state is high
CPHA=1, sample on falling
=>mode=3
But there's no 3WIRE related config, and don't know how to decide speed and lsb option.

spi-config -d /dev/spidev0.0 -m 3 -l 0 -b 8
spi-config -d /dev/spidev0.0 -q