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

On 7/3/22 6:10 pm, Milan Obuch wrote:
> On 06 Mar 2022 23:09:14 UTC
> Don Kuenz <mail@crcomp.net> wrote:
>
>> Milan wrote:
>>
>>> could you show us what's in /dev directory? Probably no iic0 file
>>> there. Also, you did not write which kernel are you using. For
>>> /dev/iic0 to appear, you need either 'device iic' in your kernel
>>> config or load it dynamically via 'kldload iic', in addition to
>>> working i2c controller.
>>>
>>> Showing your 'dmesg' output helps to determine what's going on,
>>> along with DTB used as well.
>>>
>>> All this are just basic hints what and where to look for, there are
>>> probably other as well, but I hope this helps.
>> root@generic:~ # dmesg | grep iic
>>
> OK, this means no iic device is being detected.
>
>> root@generic:~ # dmesg | grep gpio
>> gpio0: <BCM2708/2835 GPIO controller> mem 0x7e200000-0x7e2000b3 irq
>> 7,8 on simplebus0 gpiobus0: <OFW GPIO bus> on gpio0
>> gpioc0: <GPIO controller> on gpio0
>> gpioled0: <GPIO LEDs> on ofwbus0
>>
> So, you have GPUIO controller present, you should see what's available
> to control it with 'gpioctl -lv' (it uses /dev/gpioc0, which should be
> present in your system according to the dmesg snippet above).
>
>> root@generic:~ # ls /dev/iic*
>> ls: /dev/iic*: No such file or directory
>>
> This confirms what I wrote above, no iic device.
>
>> root@generic:~ # kldload iic
>> kldload: can't load iic: module already loaded or in kernel
>>
> You are probably using GENERIC kernel, judging from host name show, and
> indeed, 'device iic' is present in GENERIC kernel config.
>
>> root@generic:~ # kldstat
>> Id Refs Address        Size Name
>>   1   14 0xc0000000   d6a938 kernel
>>   2    1 0xc0d6b000    23358 gpioiic.ko
>>   3    2 0xc0d8f000    23fcc iicbb.ko
>>   4    1 0xc0db3000    24f48 umodem.ko
>>   5    2 0xc0dd8000    28328 ucom.ko
>>
> 'kldstat -v' would show more details, device iic is presented as part
> of kernel, most probably (again, judged from what you present).
>
>> FreeBSD 11.1 automatically creates /dev/iic (unsure of the suffices).
>> But 11.1 is now obsolete. FDT replaced automatic IIC bit-bang driver
>> discovery.
>> You need to "wire" FDT beforehand. Although there's hints and
>> configuration snippets all over the Inet, a full blown howto example
>> eludes me thus far.
>>
> Well, I think what Mark wrote is exactly what's needed. As I did not
> work with Raspberry a long time, I can't tell anything about config.txt
> in /boot/msdos directory (or, in another word, in FAT partition
> available for pre-FreeBSD boot loader), but I think this snippet from
> your first message should not go there:
>
>> / {
>>   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";
>>   };
>> };
> My gut feeling here is it is just being ignored because syntactically it
> does not make much sense. I may be wrong here. Do you have any pointer
> where you got this snipped from?
>
> For me it would be meaningfull if you put this snippet into a file,
> say, rpi2-gpioiic.dtso, use DTB compiler to create binary blob,
> rpi2-gpioiic.dtbo.
>
> I would create such an overlay by putting source file into
> sys/dts/arm/overlays directory and modifying Makefile in
> sys/modules/dtb/rpi directory to include rpi2-gpioiic.dtso in DTSO
> variable for appropriate MACHINE_ARCH. (As I see there now, file name
> should be gpioiic-rpi2.dtso to match the convention used here, but this
> is functionally irrelevant.)
>
> This way, overlay file would be created when doing 'make buildkernel'
> and installed in appropriate place with 'make installkernel', but it is
> possible to do just FDT overlay build, I just do not know exact
> commands from my memory.
>
> Now, when you have your overlay in /boot/dtb/overlay directory, you
> need to activate it by including its name in fdt_overlays variable in
> loader.conf file present in /boot directory, so there should be line
> like this:
>
> fdt_overlays="rpi2-gpioiic"
>
> I hope this is correct and usefull for you. It's based on my experience
> elsewhere, but this is what works for me on my boards, albeit not RPI
> (I did not use for a long time).
>
> Also, you can try 'ofwdump -a' command to see which devices should be
> present according FDT provided to system before and after doing some
> change to verify there is some effect from your changes...
>
> Regards,
> Milan
>
I think I'm like most people here, trying to guess what you are wanting 
to achieve. Pins 2 and 3 are already avalable as iic1 provided you include:

dtparam=i2c_arm

in your config.txt file. There's a little more magic needed on the rpi4 
but that doesn't effect you.

Pin 3 (GPIO 2) is SDA and Pin 5 (GPIO 3) is SCL. This 'seems' to be the 
opposite of what you are doing in your dts snippet so I could be wrong, 
but I would have thought these functions would be hardwired in the SOC.

As for your specific device, PCF8574; I don't have any direct experience 
but it looks like a standard IIC device that should work OK. I see there 
is a FreeBSD kernel module to support it but it is quite recent so 
probably only in CURRENT. As I said, I don't have experience with that 
particular device.

Hope this helps,


Brian