i2c on RPi Zero?

Sun Jan 6 07:10:03 UTC 2019

> On 6 Jan 2019, at 01:58, Emmanuel Vadot <manu at bidouilliste.com> wrote:
> 
> On Sun, 6 Jan 2019 00:39:48 +0100
> Per Hedeland <per at hedeland.org <mailto: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).
> 
> No, my take is that FreeBSD users should be able to tweak rpi the same
> way (more of less) than the Linux users. Unfortunatly, as you pointed
> out, sometimes it's hidden via a script/binary that do it for you.
> 
> But more important is that I don't want to enable i2c (or any other
> function on pins) if the board doesn't requires it. DTS/DTB is supposed
> to represent the hardware and if the hardware doesn't have i2c (or,
> again, any other stuff on some pins) there is no reason for us to
> switch by default to those functions.
> 
>> 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.
> 
> The wiki probably need a lot of updates on how to use i2c/spi or
> whatever on rpi* (with dtb overlays examples etc …).

yes, absolutely, but why only RPI*, there is also Allwinner and others,
so some ‘standard’ way should exist. It’s a moving target, fine, but some
minor doc would be nice …
SMWT — Sunday Morning Wishful Thinking

danny

> 
>> 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
> 
> Cheers,
> 
> -- 
> Emmanuel Vadot <manu at bidouilliste.com <mailto:manu at bidouilliste.com>> <manu at freebsd.org <mailto:manu at freebsd.org>>
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