i2c on RPi Zero?

[Per Hedeland]

On 2019-01-07 21:10, Ronald Klop wrote:
> On Sun, 06 Jan 2019 00:39:48 +0100, Per Hedeland <per at hedeland.org> wrote:
> 
>> On 2019-01-05 23:03, Emmanuel Vadot wrote:
>>> On Sat, 5 Jan 2019 13:56:08 -0800
>>> Oleksandr Tymoshenko <gonzo at bluezbox.com> wrote:
>>>
>>>> Per Hedeland (per at hedeland.org) wrote:
>>>>> On 2019-01-05 20:58, Oleksandr Tymoshenko wrote:
>>>>>> Per Hedeland (per at hedeland.org) wrote:
>>>>>>> I did a bit more testing on the Zero to see if the FreeBSD version
>>>>>>> mattered:
>>>>>>>
>>>>>>> FreeBSD-12.0-STABLE-arm-armv6-RPI-B-20190103-r342709.img - still no
>>>>>>> luck.
>>>>>>>
>>>>>>> FreeBSD-11.2-STABLE-arm-armv6-RPI-B-20190103-r342709.img - works!
>>>>>>> (I.e. dmesg reports as below and /dev/iic{0,1} get created - I haven't
>>>>>>> tested actual usage beyond having 'i2c -s' report "no devices found".)
>>>>>>>
>>>>>>> I guess that the i2c support hasn't been removed intentionally,
>>>>>>> i.e. this seems to be a regression - or is there some additional
>>>>>>> config etc required to enable it with FreeBSD-12? The iic and iicbus
>>>>>>> drivers appear to be built into the kernel in both 11 and 12.
>>>>>>>
>>>>>>> (I haven't tested FreeBSD-12 on the Pi B, but I would guess that the
>>>>>>> result will be the same as on the Zero, since it seems the hardware is
>>>>>>> the same.)
>>>>>>
>>>>>> There was a transition in device tree files between 11 and 12.
>>>>>> bcm2708-rpi-0-w.dtb has i2c nodes but they're disabled by default.
>>>>>> Try editing config.txt on FAT partition and adding following line:
>>>>>>
>>>>>> dtparam=i2c
>>>>>>
>>>>>> This should make boot firmware to enable device nodes in the device
>>>>>> tree blob during the boot.
>>>>>
>>>>> Thanks a lot! I can confirm that this makes i2c "work" on Zero with
>>>>> 12-RELEASE (almost) to the extent described above for 11.2-STABLE (it
>>>>> detects/creates only iic0, not iic1, but as far as I understand from
>>>>> other sources, iic0 is all that is needed for "plain B" and thus also
>>>>> for Zero).
>>>>>
>>>>> Should I file a PR for this? I assume that the i2c nodes being
>>>>> disabled is not intentional...
>>>>
>>>> Yes, please do. There are also other devices, that should be enabled by
>>>> default, like SPI.
>>>    Why should we enabled them by default ?
>>>   We have no correct way for switching a pin to gpio mode (you can do
>>> that with gpioctl on some system but I consider it as a bug) so if I
>>> want to use the i2c/spi/whatever pins as gpio and the default image set
>>> it to another function I'm stuck.
>>>   Using the rpi fundation dtb means that every settings that they set
>>> for Linux will also be set for us, so every tutorial on the web where
>>> people saying that you should set something in config.txt will apply to
>>> FreeBSD too.
>>>   The current settings aren't a bug, it's a feature (c).
>>
>> OK... - so your take seems to be that FreeBSD users should google for
>> the "Linux way" to (e.g.) enable i2c on RPi. I googled "enable i2c on
>> raspberry pi" now, and indeed it brought up lots of Linux stuff, but
>> unfortunately it mostly says to run 'raspi-config', which I can't find
>> on my FreeBSD installation (and didn't actually expect to, of course).
>>
>> If I explicitly add "config.txt" to the search string, I do indeed
>> find some info about what to put in that file - but of course I
>> wouldn't have done that if I didn't already know that this was the
>> file that needed to be edited...
>>
>> I'm all for using "standard" components (even when "standard" means
>> "Linux"), and reducing the amount of FreeBSD-specific work that you
>> and others need to put in to support FreeBSD on these "odd" systems -
>> and as a long time (Free)BSD user, I actually prefer to edit a file
>> over running some GUI tool without knowing what it does.
>>
>> But I really think there needs to be a bit more help directed
>> specifically at the FreeBSD user here (if there is and I just haven't
>> found it, please enlighten me). A few words (besides "configuration
>> for start.elf":-) about what config.txt is good for, and perhaps a
>> pointer to e.g.
>> https://www.raspberrypi.org/documentation/configuration/device-tree.md
>> (found it from your hints, thanks!), on the
>> https://wiki.freebsd.org/FreeBSD/arm/Raspberry%20Pi page may be
>> enough.
> 
> I added this to the wiki.
> https://wiki.freebsd.org/action/info/FreeBSD/arm/Raspberry%20Pi?action=diff&rev2=83&rev1=82

Great, thanks! Though AFAIU the "needs dt config" for i2c is not
specific for Zero, I believe it is disabled in all the .dtb files for
12+. E.g. from the RPI-B image:

pi0 1> dtc -I dtb -O dts /boot/msdos/bcm2708-rpi-b-plus.dtb | awk '$1~/^i2c@/ {print; ++p} p && /status/ {print; p=0}'
                 i2c at 7e205000 {
                         status = "disabled";
                 i2c at 7e804000 {
                         status = "disabled";
                 i2c at 7e805000 {
                         status = "disabled";

(guessing that those are the relevant lines:-).

--Per

> Regards,
> Ronald.
> 
>>
>> And despite the whining above, I really do appreciate all your efforts
>> to make it possible to run FreeBSD on these systems - many thanks!
>>
>> --Per Hedeland
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