RK3288 SPI 的相关寄存器详细的介绍和使用
The serial peripheral interface is an APB slave device. A four wire full duplex serial protocol
from Motorola. There are four possible combinations for the serial clock phase and polarity.
The clock phase (SCPH) determines whether the serial transfer begins with the falling edge of
slave select signals or the first edge of the serial clock. The slave select line is held high when
the SPI is idle or disabled. This SPI controller can work as either master or slave mode.
