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SPI

This document describes SPI functionality and usage.

Overview​

SPI (Serial Peripheral Interface) is a serial communication interface between the SoC (System on Chip) and peripherals, and supports only x1 mode. SPI has two modes: Master and Slave. Typically, one master device controls one or more slave devices for communication. The master device selects a slave device, completes data exchange, provides the clock, and initiates read and write operations. K3 SPI currently supports Master mode only.

Functionality​

The Linux SPI driver framework consists of three layers: SPI Core, SPI Controller Driver, and SPI Device Driver.

  • The main functions of SPI Core are:

    • Registering the SPI bus and the spi_master class
    • Adding and removing SPI controllers
    • Adding and removing SPI devices
    • Registering and unregistering SPI device drivers

  • SPI Controller Driver:

    • The SPI master controller driver, responsible for operating the SPI master controller

  • SPI Device Driver:

    • Implements communication with specific SPI peripherals

Source Code Structure​

The controller driver code is located in the drivers/spi directory:

|-- drivers/spi/spi-spacemit-k1.c              # K3 SPI driver

Key Features​

Features​

FeatureDescription
CommunicationSupports SSP/SPI/MicroWire/PSP protocols
Communication FrequencyMaximum supported frequency is 52 Mbps; minimum supported frequency is 800 Kbps
Bus Widthx1
Supported PeripheralsSupports SPI-NOR and SPI-NAND flash memory

Performance Parameters​

  • Communication Frequency
    The supported communication frequencies are 51.2M / 25.6M / 12.8M / 6.4M / 3.2M / 1.6M / 800k.

  • Bus Width
    SPI bus width supports x1.

Testing Method
Use an oscilloscope or logic analyzer to measure the SCK (Serial Clock) frequency.

Configuration​

This mainly includes Kconfig configuration and DTS configuration.

Kconfig Configuration​

CONFIG_SPI: Provides support for the SPI bus protocol. By default, this option is set to Y.

Device Drivers
		SPI support (SPI [=y])

CONFIG_SPI_K1: Provides support for the K1/K3 SPI controller driver. By default, this option is also set to Y.

Device Drivers
		SPI support (SPI [=y])
				Spacemit K1 SPI Controller (SPI_K1 [=y])

DTS Configuration​

pinctrl​

Refer to the reference design schematic to identify the pin group used by SPI. For pin configuration details, refer to PINCTRL. For example:

Assume SPI0 directly uses the ssp0_2_cfg group defined in k3_pinctrl.dtsi.

SPI Device Configuration​

When configuring an SPI device, confirm the device type and communication frequency parameters.

  • Device Type Confirm the type of device connected to the SPI bus, such as SPI-NOR or SPI-NAND.

  • Communication Frequency Specify the maximum communication rate between the SPI controller and the SPI device.

  • Communication Width SPI communication width supports x1 mode.

SPI device DTS configuration example: Using SPI NOR as an example, set the maximum communication frequency to 26 MHz, with both transmit and receive operating in x1 mode.

&pinctrl {
 ssp0-2-cfg {
  // 1V8
  ssp0-0-pins {
   power-source = <1800>;
  };
  ssp0-1-pins {
   power-source = <1800>;
  };
 };
};

&spi0 {
 pinctrl-names = "default";
 pinctrl-0 = <&ssp0_2_cfg>;
 status = "okay";

 flash@0 {
  compatible = "jedec,spi-nor";
  reg = <0>;
  spi-max-frequency = <26500000>;
  m25p,fast-read;
  broken-flash-reset;
  status = "okay";
 };

};

Interface​

API​

Device Driver Registration and Unregistration

int __spi_register_driver(struct module *owner, struct spi_driver *sdrv);  
void spi_unregister_driver(struct spi_driver *sdrv);

Data Transfer APIs

  • Initialize spi_message
void spi_message_init(struct spi_message *m);
  • Add spi_transfer to the transfer list of spi_message
void spi_message_add_tail(struct spi_transfer *t, struct spi_message *m);
  • Write data
int spi_write(struct spi_device *spi, const void *buf, size_t len);
  • Read data
int spi_read(struct spi_device *spi, void *buf, size_t len);
  • Synchronously transfer spi_message
int spi_sync(struct spi_device *spi, struct spi_message *message);

Debug​

sysfs​

View SPI bus device and driver information in the system. /sys/bus/spi

|-- devices                 // Devices on the SPI bus
|-- drivers                 // Device drivers registered on the SPI bus
|-- drivers_autoprobe
|-- drivers_probe
`-- uevent

debugfs​

Used to view SPI device information in the system. /sys/kernel/debug/spi-nor/spi0.0

Testing​

SPI NAND/NOR Read/Write Speed Test​

  1. Enable CONFIG_MTD_TESTS
Device Drivers
 Memory Technology Device (MTD) support (MTD [=y])
  MTD tests support (DANGEROUS) (MTD_TESTS [=m])
  1. Run the test command
insmod mtd_speedtest.ko dev=0   # 0 indicates the MTD device number of SPI NAND/NOR

FAQ​