Re: PCF8574 I2C configuration for 14.0-CURRENT on a RPi2B

Attempt number four to answer Mark's question in regards to the origin 
of config.txt content. (The em control character spewed out by "man" 
mangled my mail earlier.)

Mark wrote:
> Don wrote:
>>
>> and /boot/msdos/config.txt looks like this:
>> 
>> root@generic:/boot # cat /boot/msdos/config.txt
>> init_uart_clock=3000000
>> enable_uart=1
>> kernel=u-boot.bin
>> kernel7=u-boot.bin
>> dtoverlay=mmc
>
> config.txt seems fine up to here. But I've never seen
> anything indicating that the following notation is
> valid for config.txt files:
> 
>> / {
>>  gpioiic0 {
>>    compatible = "i2c-gpio";
>>    pinctrl-names = "default";
>>    pinctrl-0 = <&pinctrl_gpioiic0>;
>>    scl-gpios = <&gpio2  3 GPIO_ACTIVE_HIGH>;
>>    sda-gpios = <&gpio3  5 GPIO_ACTIVE_HIGH>;
>>    status = "okay";
>>  };
>> };
>
> If you have a reference indicating otherwise, I'd
> be interested to know what it is.

# man gpioicc

------------------------------------------------------------------------
GPIOIIC(4)	       FreeBSD Kernel Interfaces Manual 	    GPIOIIC(4)
 
NAME
     gpioiic - GPIO I2C bit-banging device driver
 
SYNOPSIS
     To compile this driver into the kernel, place the following lines in your
     kernel configuration file:
 
	   device gpio
	   device gpioiic
	   device iicbb
	   device iicbus
 
     Alternatively, to load the driver as a module at boot time, place the
     following line in loader.conf(5):
 
	   gpioiic_load="YES"
 
DESCRIPTION
     The gpioiic driver provides an IIC bit-banging interface using two GPIO
     pins for the SCL and SDA lines on the bus.

     gpioiic simulates an open collector kind of output when managing the pins
     on the bus, even on systems which don't directly support configuring gpio
     pins in that mode.  The pins are never driven to the logical value of
     '1'.  They are driven to '0' or switched to input mode (Hi-Z/tri-state),
     and an external pullup resistor pulls the line to the 1 state unless some
     other device on the bus is driving it to 0.
 
HINTS CONFIGURATION

<snipped>

FDT CONFIGURATION
     On an FDT(4) based system, such as ARM, the DTS node for gpioiic conforms
     to the standard bindings document i2c/i2c-gpio.yaml.  The device node
     typically appears at the root of the device tree.	The following is an
     example of a gpioiic node with one slave device on the IIC bus:

     / {
	     gpioiic0 {
		     compatible = "i2c-gpio";
		     pinctrl-names = "default";
		     pinctrl-0 = <&pinctrl_gpioiic0>;
		     scl-gpios = <&gpio1  5 GPIO_ACTIVE_HIGH>;
		     sda-gpios = <&gpio7 11 GPIO_ACTIVE_HIGH>;
		     status = "okay";

		     /* One slave device on the i2c bus. */
		     rtc@51 {
			     compatible="nxp,pcf2127";
			     reg = <0x51>;
			     status = "okay";
		     };
	     };
     };

     Where:

     compatible      Should be set to "i2c-gpio".  The deprecated string
		     "gpioiic" is also accepted for backwards compatibility.

     scl-gpios sda-gpios
		     These properties indicate which GPIO pins should be used
		     for clock and data on the GPIO IIC bit-banging bus.
		     There is no requirement that the two pins belong to the
		     same gpio controller.

     pinctrl-names pinctrl-0
		     These properties may be required to configure the chosen
		     pins as gpio pins, unless the pins default to that state
		     on your system.

SEE ALSO
     fdt(4), gpio(4), iic(4), iicbb(4), iicbus(4)

------------------------------------------------------------------------

I'll take a closer look at "man dtc" and "i2c/i2c-gpio.yaml"

https://mjmwired.net/kernel/Documentation/devicetree/bindings/i2c/i2c-gpio.yaml

Other replies in the thread provide me with additional food for thought
for the time being.

Danke,

-- 
Don, KB7RPU, https://www.qsl.net/kb7rpu
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.