Add CAN support

[manchoz]

It would be nice to integrate CAN bus support in the build, either as integrated drivers or modules.

There are many CAN adapters based on different HW bus technologies, starting from UARTs to SPI. Pretty popular, inexpensive, and open source devices include CAN USB adapters like CANable and Candlelight, which are supported by the slcan and gs_usb drivers, respectively. PEAK System PCAN-USB adapters are also popular and considered one of the reference implementations.

[lool]

Thanks for listing specific USB devices that we want to enable (CANable and Candlelight); is this request about turning tweaking the kernel config? Could you list the specific minimum changes that would be needed?

Once we make these changes, someone plugs their USB device and it works? Are any other software changes needed?

[quaresmajose]

Thanks for listing specific USB devices that we want to enable (CANable and Candlelight); is this request about turning tweaking the kernel config? Could you list the specific minimum changes that would be needed?

Yes, this requires kernel config changes. We need to add the socketcan networks stack as well as some IO driver to look at the electrical signals on the bus.

Once we make these changes, someone plugs their USB device and it works? Are any other software changes needed?

We need some user space tools like the canutils but I can investigate more to understand the satus of the can bus on linux.
The slcan is to attach can drivers that comunicates over rs232, the gs_usb is a new tool for me.

[manchoz]

Yes, this requires kernel config changes. We need to add the socketcan networks stack as well as some IO driver to look at the electrical signals on the bus.

Once we make these changes, someone plugs their USB device and it works? Are any other software changes needed?

Depending on the driver, i.e., the attached device, some command needs to be issued to create the CAN interface. Being CAN supported in a similar way to networking devices (because of SocketCAN), interfaces can be configured with iproute tools such as ip.

The can-utils package is recommended.

We need some user space tools like the canutils but I can investigate more to understand the satus of the can bus on linux. The slcan is to attach can drivers that comunicates over rs232, the gs_usb is a new tool for me.

slcan is for devices which expose an UART interface towards the host over which the slcand daemon creates a CAN interface. gs_usb is used with the Candlelight firmware and is natively SocketCAN compatible. Every CAN devices then attaches to a CAN bus (which is typically made by three wires, CANH, CANL, and GND.)

[lool]

Revisiting this after being distracted for a little bit, I also had the chance to sleep on this and think about the request.

We think people using Qualcomm based hardware / reference images might want to play with USB accessories that provide a CAN bus. The idea is not specific to Qualcomm hardware, this would make sense on e.g. a RPi as only a USB port is required to do what is described here.

This is where we currently define the kernel configs and the userspace selection that goes into our reference images for developers, so we're keen to:

• make sure our kernels support these scenarios
• make sure the right userspace is installed out of the box

There are essentially two types of kernels we support:

1. some are based on the Debian kernel config + a few changes
2. some are based on the upstream defconfig + a few changes

Would someone be able to list the minimal kernel configs we need to turn on for 1) and for 2)? We want these to create kernel config fragments for these like these:
https://github.com/qualcomm-linux/qcom-deb-images/tree/main/kernel-configs
#147

We should also upstream changes for 1) if any to Debian.

For the rootfs, we can tackle it after we address the kernel config, but a simple pull request against the rootfs.yaml debos recipe listing the new package would probably fine. I'm pretty sure it's going to be small non-invasive packages (apparently just can-utils which only depends on libc6), so we can add them with a comment for instance here:

qcom-deb-images/debos-recipes/qualcomm-linux-debian-rootfs.yaml

Line 166 in ab42026

- action: apt

[lool]

@manchoz mentioned he had success with this fragment:

$ cat kernel-configs/can.config 
CONFIG_CAN_SLCAN=y
CONFIG_CAN_GS_USB=y
CONFIG_CAN_PEAK_USB=y

He added: "SLCAN and GS_CAN are for the open source CANable and Candlelight projects (and derivatives); PEAK is for PEAK USB which is one of the most popular profesional USB to CAN adapter"