Example Use Case

The following section lists a typical use case of JH7110 SPI.

Locating the Original Kernel Driver

The driver file is stored in the following path. 
freelight-u-sdk/linux/drivers/spi/spidev.c

The driver is a Linux embedded SPI device driver.

Registering an SPI Driver

You can use the spi_register_driver interface to register an SPI driver, as a basis for SPI message reading and writing.

The following code block provides an example. 
static int __init spidev_init(void)
{
	int status;

	/* Claim our 256 reserved device numbers.  Then register a class
	 * that will key udev/mdev to add/remove /dev nodes.  Last, register
	 * the driver which manages those device numbers.
	 */
	BUILD_BUG_ON(N_SPI_MINORS > 256);
	status = register_chrdev(SPIDEV_MAJOR, "spi", &spidev_fops);
	if (status < 0)
		return status;

	spidev_class = class_create(THIS_MODULE, "spidev");
	if (IS_ERR(spidev_class)) {
		unregister_chrdev(SPIDEV_MAJOR, spidev_spi_driver.driver.name);
		return PTR_ERR(spidev_class);
	}

	status = spi_register_driver(&spidev_spi_driver);
	if (status < 0) {
		class_destroy(spidev_class);
		unregister_chrdev(SPIDEV_MAJOR, spidev_spi_driver.driver.name);
	}
	return status;
}
module_init(spidev_init);

Configuring the SPI Driver

In the meantime, make sure you have added device information descriptions of the sub-devices for the SPI controller in the dts file.

The following code block shows an example of spi0. 
&spi0 {
        pinctrl-names = "default”;
        pinctrl-0 = <&ssp0_pins>;
        status = "disabled";
        spi_dev0: spi@0 {
        compatible = "rohm,dh2228fv";
        pl022,com-mode = <1>;
        spi-max-frequency = <10000000>;
        reg = <0>;
        status = "okay";
};
The configuration file contains the following parameters for spi_dev0.
  • compatible: The compatibility information of the driver.
  • pl022,com-mode: The communication mode of the driver. The following values are available.
    • 0: Polling.
    • 1: Interrupt
    • 2: DMA
  • spi-max-frequency: The maximum frequency of the slave device.
    Note: Make sure you set the a proper value for maximum frequency based on your real conditions, data loss in transmission maybe caused if an improper value is configured.
  • reg: The register address offset of the slave device.
  • status: Status of the slave device. The following values are available.
    • okay: The slave device is working properly.
    • disabled: The slave device has been disabled.

Configuring Kernel Menu

In the kernel menu configuration, make sure you have selected the User mode SPI device driver support option.
Figure 1. User Mode SPI Support

Building the SPI File

After you have completed the firmware installation, follow the steps below to build the SPI file.
  1. Find the spidevX.0 (X = 1-7) device under the /dev folder.
  2. Perform reading and writing operations on the file. Or you can use the Linux SPI tool, and run the following command under path: 
    freelight-u-sdk/linux/tools
  3. Use the following command to build SPI file for test. 
    # make spi

    Result: An executable file named spidev_test is generated under the freelight-u-sdk/linux/tools/spi path.

Testing the SPI File

Follow the steps below to test your generated SPI file.
  1. Copy the generated file to the SoC and connect the TX and RX of the I/O port on the SPI.
  2. Then run the following command to test:
    #  /spidev_test -D /dev/spidevX.0 -v -p data
    Result: The displayed data is the content to be transferred. The test example is as follows.
    Figure 2. SPI Test Example