SC16IS752 Driver not reporting Modem control correctly on PI model 4

[mtnbarn]

Describe the bug

The modem signal lines are not being reported properly on the Raspberry PI 4. RTS,CTSDSR,DCD,DTR and RI are always reported as true using statserial. PI 3-B 1.2 and PI 2-B 1.2 report status and change in status correctly. RX/TX seem to work properly on all.

Steps to reproduce the behaviour

Run "statserial /dev/ttySC0" on PI 4 with sc16is752 attached via spi.
(All lines are NOT asserted)

output
Device: /dev/ttySC0

Signal Pin Pin Direction Status Full
Name (25) (9) (computer) Name

---

FG 1 - - - Frame Ground
TxD 2 3 out - Transmit Data
RxD 3 2 in - Receive Data
RTS 4 7 out 1 Request To Send
CTS 5 8 in 1 Clear To Send
DSR 6 6 in 1 Data Set Ready
GND 7 5 - - Signal Ground
DCD 8 1 in 1 Data Carrier Detect
DTR 20 4 out 1 Data Terminal Ready
RI 22 9 in 1 Ring Indicator

Device (s)

Raspberry Pi 4 Mod. B

System

root@raspberrypi:/home/pi# cat /etc/rpi-issue
Raspberry Pi reference 2023-05-03
Generated using pi-gen, https://github.com/RPi-Distro/pi-gen, 638c7521ee0c431fafca1e2bd4fd25705b37ea5b, stage2

root@raspberrypi:/home/pi# vcgencmd version
Mar 17 2023 10:50:39
Copyright (c) 2012 Broadcom
version 82f3750a65fadae9a38077e3c2e217ad158c8d54 (clean) (release) (start)

root@raspberrypi:/home/pi# uname -a
Linux raspberrypi 5.10.103-v8+ #1529 SMP PREEMPT Tue Mar 8 12:26:46 GMT 2022 aarch64 GNU/Linux

Logs

No response

Additional context

No response

[pelwell]

I don't understand why you have submitted a patch against rpi-6.1.y (our current branch) and now are reporting a problem with the same driver but on 5.10? What happens on rpi-6.1.y?

My sc16is752 board is I2C-based, but running on a 4B I can see the CTS level going high when the pin is grounded. If you want to debug this further you should enable SPI logging:

1. Enable SPI tracing:

$ sudo sh -c "echo 1 >/sys/kernel/debug/tracing/events/spi/enable"

2. Run statserial, changing at least the CTS level.

3. Capture the tracing output:

$ sudo cat /sys/kernel/debug/tracing/trace > spi_log1.txt

4. If you want to run another test without rebooting, first clear the trace so far:

$ sudo sh -c "echo >/sys/kernel/debug/tracing/trace"

Run that test on both systems - Pi 4 and Pi 3, capturing the log to a different (and ideally suitably named) file each time.