Custom SPI protocol kernel module and device tree

[Георгий Одишария]

Hello. I have trouble trying to get information from DT in my kernel module.

I made and built device tree overlay similar to one for spidev kernel module. Here it is:

/dts-v1/;
/plugin/;


/ {
    compatible = "ti,beaglebone", "ti,beaglebone-black";


    /* identification */
    part-number = "BB-ARDUINO-ECHO";
    version = "00A0";
 
    fragment@0 {
        target = <&am33xx_pinmux>;
        __overlay__ {
            spi0_pins_s0: spi0_pins_s0 {
 pinctrl-single,pins = <
 0x150 0x30      /* mcasp0_aclkx.spi0_sclk, INPUT_PULLUP  | MODE0 */
 0x154 0x30      /* mcasp0_fsx.spi0_d0,     INPUT_PULLUP  | MODE0 */
 0x158 0x10      /* mcasp0_axr0.spi0_d1,    OUTPUT_PULLUP | MODE0 */
 0x15c 0x10      /* mcasp0_ahclkr.spi0_cs0, OUTPUT_PULLUP | MODE0 */
 >;
            };
        };
    };


    fragment@1 {
        target = <&spi0>;
        __overlay__ {


            #address-cells = <1>;
            #size-cells = <0>;
            status = "okay";
            pinctrl-names = "default";
            pinctrl-0 = <&spi0_pins_s0>;
           
            ardiuno_echo@0 {
                compatible = "arduino,pro-mini-spi-generic";
                reg = <0>;
                spi-max-frequency = <100000>;
            };
        };
    };
};

And here I trying to access spi-max-frequency property from my probe() function of device driver:

static int spi_protocol_generic_probe(struct spi_device *spi)
{
 int err, ret;
 int devData = 0;
 const struct of_device_id *match;


 struct device_node *of_target_node;
 u32 max_speed_arduino = 0;


 const char *of_compt_str = kcalloc(sizeof(char), 255, GFP_KERNEL);


 __spi_device_internal = spi;
 default_values.speed_hz = spi->max_speed_hz;
 default_values.mode = spi->mode;
 default_values.bits_per_word = spi->bits_per_word;


 debug_printk("spi-protocol-generic: default speed is %d Hz\n",
     default_values.speed_hz);


 // check and read data from of_device_id...
 match = of_match_device(spi_protocol_generic_of_match, &spi->dev);
 if (!match) {
 debug_printk("device not found in device tree...\n");
 return -1;
 }
 of_target_node = of_find_compatible_node(NULL, NULL, match->compatible);
 if (!of_target_node) {
 of_node_put(of_target_node);
 debug_printk("no compatible devices in DT!\n");
 }


 // Here we can use of_get_property, but I prefer more readable
 // code insted of mire obvious
 ret = of_property_read_u32(of_target_node, "spi-max-frequency",
   &max_speed_arduino);


 if (ret) {
 debug_printk("cannot find property in DT node, status %d\n",
     ret);
 return ret;
 } else {
 debug_printk("freq is %x Hz\n", max_speed_arduino);
 }


 spi->bits_per_word = 8;
 spi->mode = SPI_MODE_0;
 spi->max_speed_hz = max_speed_arduino;
 err = spi_setup(spi);


 if (err < 0) {
 printk(KERN_DEBUG "spi-protocol-generic: spi_setup failed!\n");
 return err;
 } else {
 printk(KERN_DEBUG "spi-protocol-generic: now speed is %d Hz\n",
       spi->max_speed_hz);
 }
        // ... and so on ...
}

I can access other properties such as reg and compatible. But even if I am trying to get the property of DT from sysfs, this property seems to have invalid value.

For example, if I set spi-max-frequency to 1000000 (1 MHz), value from sysfs will be invalid and it won't equal 1000000. This value is not depending from my value in DT overlay.

How can I set this property correctly?

[Георгий Одишария]

Also:

root@arm:~# cat /sys/bus/spi/devices/spi1.0/of_node/spi-max-frequency | hexdump
0000000 6e01 0036                               
0000004