6.12.34 breaks Waveshare RS232 HAT

[ronnybremer]

Describe the bug

After upgrading from 6.12.20 to 6.12.34 the Waveshare overlay still gets loaded, however, communication via ttySC1 is no longer possible, the user app just freezes.

dmesg output for 6.12.34

[    4.693022] sc16is7xx spi1.0: Native CS is not supported - please configure cs-gpio in device-tree
[    4.697683] spi1.0: ttySC0 at I/O 0x0 (irq = 59, base_baud = 921600) is a SC16IS752
[    4.701597] spi1.0: ttySC1 at I/O 0x1 (irq = 59, base_baud = 921600) is a SC16IS752

dmesg output for 6.12.20

[    5.635965] spi1.0: ttySC0 at I/O 0x0 (irq = 44, base_baud = 921600) is a SC16IS752
[    5.636656] spi1.0: ttySC1 at I/O 0x1 (irq = 44, base_baud = 921600) is a SC16IS752

The config.txt snippet to load the overlay:

dtoverlay=sc16is752-spi1,int_pin=24

Steps to reproduce the behaviour

Upgrade kernel to 6.12.30, try to communicate with /dev/ttySC1, notice the app freezes and the activity LEDs on the Waveshare don't blink

Downgrade to kernel 6.12.20, communication is fine and activity LEDs blink as expected

Device (s)

Raspberry Pi 4 Mod. B

System

PRETTY_NAME="Debian GNU/Linux 12 (bookworm)"
NAME="Debian GNU/Linux"
VERSION_ID="12"
VERSION="12 (bookworm)"
VERSION_CODENAME=bookworm
ID=debian
HOME_URL="https://www.debian.org/"
SUPPORT_URL="https://www.debian.org/support"
BUG_REPORT_URL="https://bugs.debian.org/"

Firmware:
Apr 30 2025 13:33:39
Copyright (c) 2012 Broadcom
version 5560078dcc8591a00f57b9068d13e5544aeef3aa (clean) (release) (start)

Kernel (working):
6.12.20+rpt-rpi-v8

Kernel (failing):
6.12.34+rpt-rpi-v8

Logs

No response

Additional context

No response

[6by9]

#6865 is likely the cause.

[ronnybremer]

Interesting. Just reading through the changed files in the PR it looks like a warning should have been issued when loading the older overlay, which I don't remember seeing in dmesg at all.

I'll try the new overlay on a test setup and report back here.

Thanks @6by9 !

[6by9]

The old sc16is752-spi1 overlay included
cs-gpios = <&gpio 18 1>;
in the spi1 node. The new overlay doesn't set that which explains the error.

The deprecation warning ends up in device tree, although I forget exactly where. Raspberry Pi OS desktop should show you the warning in the top right just after it boots. It should also be in the firmware logs via sudo vclog -m.

edit: Should be in /proc/device-tree/chosen/user-warnings

[ronnybremer]

I am not proficient with overlays at all. Unfortunately, my PIs are all neatly tucked away on walls and in cabinets so SSH is the only access available. Which means no GUI, so no warnings ...

But thank you for the device-tree tip, I will definitely check for that as my post-update routine.

As I am unable to assist with the code change, shall we ping the PRs maintainer or will they pick it up from here?

[nbuchwitz]

I will have a look ...

[nbuchwitz]

#6964 might fix your issue.

You can either built the overlay file yourself (see https://www.raspberrypi.com/documentation/computers/linux_kernel.html#native-build, skip build of Image.gz and modules and just go for the dts target) or use this pre-compiled file: sc16is75x-spi.dtbo.txt

(make sure to remove the .txt suffix - github wont let me upload the file with .dtbo ending ...)

Make sure that you have a way to recover if something went sideways. Then just copy the file to /boot/firmware/overlays and reboot.

[ronnybremer]

Thank you @nbuchwitz, I will test this new overlay on a staging device on Sunday and let you know.

[6by9]

The easiest way to test a kernel PR on Raspberry Pi OS is to use sudo rpi-update pulls/<PR-num>, eg sudo rpi-update pulls/6964 in this case.

I've just approved the CI builds, so they should be complete in about 40mins.

[nbuchwitz]

Thanks

[ronnybremer]

@6by9 Finally got my hands on a test device, they seem to be in high demand. Installed the latest kernel, didn't work as expected. Tried the rpi-update command, but it doesn't seem to work.

 *** Raspberry Pi firmware updater by Hexxeh, enhanced by AndrewS and Dom
 *** Performing self-update
 *** Relaunching after update
 *** Raspberry Pi firmware updater by Hexxeh, enhanced by AndrewS and Dom
FW_REV:
BOOTLOADER_REV:2349daafacfb7a7abe2cfecf30a49ae837bdf2c6
 *** We're running for the first time
 *** Backing up files (this will take a few minutes)
 *** Remove old firmware backup
 *** Backing up firmware
 *** Remove old modules backup
 *** Backing up modules 6.12.34+rpt-rpi-v8
WANT_32BIT:0 WANT_64BIT:1 WANT_64BIT_RT:0 WANT_PI4:1 WANT_PI5:1
Downloading bootloader tools
Downloading bootloader images
 *** Downloading specific artifact revision (this will take a few minutes)
curl  -L https://builds.raspberrypi.com/github/linux/f1c00a6ce0508f721799985572499d0a4b2cdaf1/bcmrpi | zcat | tar xf - -C //root/.rpi-firmware --strip-components=2
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:--  0:00:04 --:--:--     0

gzip: stdin: unexpected end of file
tar: This does not look like a tar archive
tar: Exiting with failure status due to previous errors
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:--  0:00:04 --:--:--     0
Invalid artifact specified. Response: 404.

Did the pull request change?

[nbuchwitz]

The PR pipeline needs to be approved again, so the build gets updated. Besides that, if you update /boot/firmware/config.xt like this, it should also work:

dtoverlay=spi1-1cs,cs0_spidev=off
dtoverlay=sc16is75x-spi,sc16is752,spi1-0,int_pin=24