How to use SPI with gokrazy?

[x86ed]

I want to enable SPI, UART and I2C on my raspberry pi but it's not clear what commands/config I need to do to enable it on my board through gok

[stapelberg]

Hey @x86ed!

If you want to make changes to the kernel, use a modified version of https://github.com/gokrazy/kernel/, like you would swap out any other Go package: https://gokrazy.org/development/modules/#building-local-code-the-replace-directive

The kernel build we use stores its kernel config in cmd/gokr-build-kernel/build.go. It might be more convenient to use ARCH=arm64 make menuconfig in a separate checkout of the Linux kernel to figure out which config options you need/want to change.

In general, we accept changes to the kernel repository, as long as they don’t have adverse affects for other users (e.g. require hard-to-maintain patches, or disable other features that people rely on). UART is already enabled, and hopefully SPI and I2C should be quick and uncontroversial, I think…?

Hope this helps

[damdo]

Ahh it looks like you beat me to that @stapelberg :)

[damdo]

Hey, those configs must be set in the Linux kernel configuration we define for gokrazy, unless they are already.

Here, for example, we have the configuration to enable the I2C and the SPI support in the kernel:
https://github.com/gokrazy/kernel/blob/b015f4d0ae408c30b52679aa27399e281ed7c149/cmd/gokr-build-kernel/build.go#L23-L25
The recommended way to interact with those buses is to use the periph.io libs.

To my knowledge, the UART serial console is also enabled (if that's what you are looking for), see: https://github.com/gokrazy/tools/blob/231dea4b57042ff090c0a94fa03abe1dab9e3a3f/internal/packer/write.go#L76
You can tweak its config with: https://gokrazy.org/userguide/instance-config/#serialconsole

[x86ed]

Oops I'm an idiot I'm looking for SPI not i2c

[stapelberg]

Is this code known working on a Raspbian installation? If no, try that first. If yes, does it work on Debian or Fedora (not Raspbian) as well?

If yes, can you compare the strace output between Raspbian, Debian/Fedora and gokrazy? I’m wondering which driver the respective OSes use. Raspbian might have a custom kernel driver that works differently from upstream Linux’s, and what’s enabled in gokrazy might be yet another subset of that.

[x86ed]

#47 I found this old PR that I believe should fix the issue but, the PR doesn't provide the code or kernel configuration the author used to test the SPI port. I assume they used periph.io given the stack trace in the thread they posted.

Typically a program called raspi-config repo is used to set the kernel configuration in raspbian. I've used this in the past with go/periph on raspbian to connect to SPI ports. My biggest hunch is that I'm missing a configuration task on the kernel setup that should enable it. But I'm really new to altering Kernel configuration so I'm kinda unsure what i should be looking for with strace and how to run it.

[stapelberg]

The pull request you linked to was merged years ago, so I was confused why you were still running into issues.

But now that you mention raspi-config, I found https://www.raspberrypi-spy.co.uk/2014/08/enabling-the-spi-interface-on-the-raspberry-pi/, which says that config.txt (the early boot firmware configuration) should contain dtparam=spi=on.

We currently don’t offer a way to customize what goes into config.txt in gokrazy. However, you can clone the gokrazy kernel repository and manually edit config.txt (see also https://gokrazy.org/development/modules/#building-local-code-the-replace-directive). Try making that change and see if that helps.

[stapelberg]

By the way, we now do have a way to customize config.txt: https://gokrazy.org/userguide/instance-config/#bootloader

[x86ed]

I cloned the kernel, added it to my gokrazy install and added the following lines to the config.txt

dtparam=spi=on

dtoverlay=spi1-1cs #enables SPI1 with 1 chip select
dtoverlay=spi1-2cs #enables SPI1 with 2 chip selects
dtoverlay=spi1-3cs #enables SPI1 with 3 chip selects

ran breakglass and did a ls /dev
got

autofs           loop1            ptyp0            serial0          tty20            tty37            tty53            ttyp1            vcs1
bus              loop2            ptyp1            shm              tty21            tty38            tty54            ttyp2            vcs2
cec0             loop3            ptyp2            snapshot         tty22            tty39            tty55            ttyp3            vcsa
console          loop4            ptyp3            snd              tty23            tty4             tty56            ttyp4            vcsa1
cpu_dma_latency  loop5            ptyp4            tty              tty24            tty40            tty57            ttyp5            vcsa2
dri              loop6            ptyp5            tty0             tty25            tty41            tty58            ttyp6            vcsu
fb0              loop7            ptyp6            tty1             tty26            tty42            tty59            ttyp7            vcsu1
full             mem              ptyp7            tty10            tty27            tty43            tty6             ttyp8            vcsu2
fuse             mmcblk0          ptyp8            tty11            tty28            tty44            tty60            ttyp9            vfio
gpiochip0        mmcblk0p1        ptyp9            tty12            tty29            tty45            tty61            ttypa            vga_arbiter
hwrng            mmcblk0p2        ptypa            tty13            tty3             tty46            tty62            ttypb            watchdog
i2c-0            mmcblk0p3        ptypb            tty14            tty30            tty47            tty63            ttypc            watchdog0
i2c-1            mmcblk0p4        ptypc            tty15            tty31            tty48            tty7             ttypd            zero
i2c-2            net              ptypd            tty16            tty32            tty49            tty8             ttype
kmsg             null             ptype            tty17            tty33            tty5             tty9             ttypf
kvm              port             ptypf            tty18            tty34            tty50            ttyAMA0          uinput
loop-control     ptmx             random           tty19            tty35            tty51            ttyS0            urandom
loop0            pts              rfkill           tty2             tty36            tty52            ttyp0            vcs

lsmod yields:

brcmfmac_wcc 16384 0 - Live 0xffffd5b1dd27e000
brcmfmac 266240 1 brcmfmac_wcc, Live 0xffffd5b1dd239000
brcmutil 16384 1 brcmfmac, Live 0xffffd5b1dd232000

there don't appear to be any spi entries. anything i can do to troubleshoot that?

[stapelberg]

I don’t know what exactly you mean with “loading the dtoverlay command with gokrazy”, but I’ll say no. We currently don’t have a way to influence config.txt in gokrazy.

[damdo]

Hey @x86ed were you able to make SPI work in the end?
I'm interested in using it to pilot an SPI display in gokrazy, which I think it is similar to what you were attempting.

[stapelberg]

By the way, we now do have a way to customize config.txt: https://gokrazy.org/userguide/instance-config/#bootloader

[x86ed]

@damdo I didn't but I do want to explore the above. The issue I ran into was trying to replicate the bios settings in go crazy without having raspi-config just ended up spnning my wheels as I'm a bit out of my depth.

[x86ed]

@stapelberg will try to attempt using this later, to see if i can unblock myself