search

raspberrypi / linux

Kernel source tree for Raspberry Pi-provided kernel builds. Issues unrelated to the linux kernel should be posted on the community forum at https://forums.raspberrypi.com/
Other
11.14k stars 4.99k forks source link

For rpi4 allow dtoverlay i2c-rtc use i2c5 port #4892

Open andres53016 opened 2 years ago

andres53016 commented 2 years ago

Describe the bug

Add functionality for dtoverlay i2c-rtc to use i2c 5 port

Steps to reproduce the behaviour

The only way to use an rtc on port 5 is activating i2c5 and run at boot, the following

echo ds1307 0x68 > /sys/class/i2c-adapter/i2c-5/new_device

Device (s)

Raspberry Pi 4 Mod. B

System

Linux alarmpi 5.15.21-3-rpi-ARCH #1 armv7l GNU/Linux

Logs

No response

Additional context

No response

pelwell commented 2 years ago

Adding the additional I2C ports to the existing i2c-rtc overlay would break it on non-BCM2711 devices - the symbol i2c5 (for example) doesn't exist in non-BCM2711 Device Trees, so the overlay cannot be applied. There is a way around the problem - create another overlay called i2c-rtc-pi4 that supports the additional interfaces, and use the overlay_map file to load the appropriate one - but it isn't particularly elegant, and would benefit from a better way to document that some parameters are only available on Pi 4s. I'm not ruling out your request, but I'd rather have some time to think about it first.

However, I can give you a version of the overlay that's been modified to work on i2c5 instead: i2c5-rtc.dtbo.zip It was hacked together with a hex editor, but it should do the job.

andres53016 commented 2 years ago

I didn't know all that the change encompassed. Thank you very much for the quick response and for the modified file. It worked perfectly

seamusdemora commented 2 years ago

Good news! I'll look forward to learning of your final solution. And this raises another question I've had: Currently, we can only access one of the two alarm registers available in the DS3231. I've always assumed that's a limitation of the driver, not the overlay... is that a correct assumption? IOW, I guess the overlay would also need to be modified to support both alarms, but the driver modification is also required, is it not?

pelwell commented 2 years ago

FYI, https://github.com/raspberrypi/linux/commit/1131d880f3917c697abd64f1c79ddd8a9611286b (not yet in an rpi-update release) adds the parameters i2c3, i2c4, i2c5 and i2c6 to the i2c-rtc overlay (and others). To avoid the problem of unresolved symbols it makes use of target-path, with the path strings consisting of the DT aliases i2c3-i2c6.