Add overlay for Seeed Studio CAN BUS FD HAT

[menschel]

This PR relates to #4032

This patch adds the overlay for the Seeed Studio CAN BUS FD HAT
with two CAN FD Channels and an RTC.
https://www.seeedstudio.com/CAN-BUS-FD-HAT-for-Raspberry-Pi-p-4742.html

The overlay was generated by

ovmerge -c mcp251xfd-overlay.dts,spi0-0,interrupt=25 \
           mcp251xfd-overlay.dts,spi0-1,interrupt=24 \
           i2c-rtc-overlay.dts,pcf85063

The overlay was tested on rpi zero w.

$ dmesg | grep -Ei can\|spi\|rtc
[   29.729815] CAN device driver interface
[   29.751296] spi_master spi0: will run message pump with realtime priority
[   29.766387] mcp251xfd spi0.1 can0: MCP2518FD rev0.0 (-RX_INT -MAB_NO_WARN +CRC_REG +CRC_RX +CRC_TX +ECC -HD c:40.00MHz m:20.00MHz r:17.00MHz e:0.00MHz) successfully initialized.
[   29.791519] mcp251xfd spi0.0 can1: MCP2518FD rev0.0 (-RX_INT -MAB_NO_WARN +CRC_REG +CRC_RX +CRC_TX +ECC -HD c:40.00MHz m:20.00MHz r:17.00MHz e:0.00MHz) successfully initialized.
[   29.899859] mcp251xfd spi0.1 mcp1: renamed from can0
[   29.919640] mcp251xfd spi0.0 mcp0: renamed from can1
[   30.158817] rtc-pcf85063 1-0051: registered as rtc0

[menschel]

Note:
There is actually one issue with this board. During enumeration the can interfaces come out in wrong order, so there is the necessity to swap both. This is done by udev rule in my case.

SUBSYSTEM=="net", ACTION=="add", DEVPATH=="/devices/platform/soc/*/*/*/spi0.0/net/can?", NAME="mcp0"
SUBSYSTEM=="net", ACTION=="add", DEVPATH=="/devices/platform/soc/*/*/*/spi0.1/net/can?", NAME="mcp1"

It would be more feasible to correct the order in dt overlay. Is there an easy way to achieve this?

I know of aliases but do they work with network device naming, not only /dev/$ALIAS ?

Another thought, should I add a paragraph about #4032 in the README ?

[menschel]

Added a proposal for describing the contents of #4032 in README

[pelwell]

There are a few formatting issues with the README, but otherwise I'm happy with this.

[marckleinebudde]

Hello,

I know that I'm late to the party, buy there are two seed studio can-fd hats. The older one has two mcp2517fd chips, one connected to spi0-0, the other to spi1-0, while the new one has two mcp2518fd chips on spi0-0 and spi0-1. Can we rename this overlay to include mcp2518fd in the name?

[menschel]

I think the correct way would be to distinguish by version number but after reading my version this seems unlikely a solution.

On the bottom side of my (mcp2518fd) board, it reads

CAN-BUS(FD) HAT for Raspberry Pi
www.seeedstudio.com
v1.0 6/20/2020

[marckleinebudde]

My mcp2517fd (https://www.seeedstudio.com/2-Channel-CAN-BUS-FD-Shield-for-Raspberry-Pi-p-4072.html) board says:

2-Channel CAN-BUS(FD) Shield
for Raspberry Pi (MCP2517FD)
www.seeedstudio.com
v1.0 1/8/2019

My mcp2518fd board says:

2-Channel CAN FD Master
HAT for Raspberry Pi
www.seeedstudio.com
v1.0 2/28/2020

Same version number, different date...

I'm using the following overlays:

# Seeedstudio CAN-BUS FD 2517FD
#dtoverlay=spi1-1cs
#dtoverlay=mcp251xfd,spi0-0,interrupt=25
#dtoverlay=mcp251xfd,spi1-0,interrupt=24

# Seeedstudio CAN-BUS FD 2518FD
#dtoverlay=mcp251xfd,spi0-0,interrupt=25
#dtoverlay=mcp251xfd,spi0-1,interrupt=24

Which means both mcp2518fd variants are compatible (at least when it comes to SPI, I haven't checked the I2C).

[menschel]

We could label these v1, v2 and v3 and add the link in README for reference.

If the Master HAT has the same RTC we get away with v1 and v2.

[menschel]

I did some experimenting and came to the conclusion that an overlay generated by

ovmerge -c spi1-1cs-overlay.dts \
           mcp251xfd-overlay.dts,spi0-0,interrupt=25 \
           mcp251xfd-overlay.dts,spi0-1,interrupt=24 \
           mcp251xfd-overlay.dts,spi1-0,interrupt=24 \
           i2c-rtc-overlay.dts,pcf85063

works with my board. Seems the "not there" device is just skipped.

It may not be a clean solution but if this works on the other boards, we may get away with one overlay.

[marckleinebudde]

IMHO this is not an option, as it enables spi1-1cs unconditionally. Better make it two overlays. Either with -v1, -v2 or with -mcp2517fd, -mcp2518fd.

[menschel]

I'm fine with the -v1, -v2 naming. Feel free to open the next PR and change the naming as appropriate.

[marckleinebudde]

Here's the pull request: #4041