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

On 2022-Mar-7, at 06:48, Don Kuenz <mail@crcomp.net> wrote:

> 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

config.txt is not something from FreeBSD at all, its
is from/for RPi* firmware only and is common across all
contexts that use the RPi* firmware. Only RPi* specific
documentation applies to the content supported in
config.txt on the msdos file system for an RPi*.

In other words: man gpioicc does not in any way refer
to the config.txt file involved in booting an RPi*
(for any operating system). To my knowledge no FreeBSD
man page covers much about files that are specific to
the RPi* firmware (ignoring, say, drivers strictly
specific to RPi* contexts).

> ------------------------------------------------------------------------
> 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";
> 		     };
> 	     };
>     };

This document does not say where the above text would
go for any system or what toolchain (if any) is involved
in putting it to use.

There can even be issues like the RPi* firmware and
FreeBSD kernel disagreeing about .dtb content and
the like. The FreeBSD firmware is still somewhat active
when FreeBSD runs as I understand. If true, it could
be important to have the RPi* firmware have the same
.dtb context as the kernel, normally by updating what
the RPi* firmware uses and letting the kernel
(indirectly) get its dtb information from the RPi*
firmware.

(I mention that because, if I remember right, one of
the replies proposed working strictly on the FreeBSD
side. I'm not sure such is appropriate to an RPi*.
However, I'm not an expert.)

>     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.
> 



===
Mark Millard
marklmi at yahoo.com