[Pi 5] i2c conflicts with MIPI

[joaoantoniocardoso]

On the Pi 4, the GPIO pins 22 and 23 map to i2c6 (ref).

However, on Pi 5:

• The i2c6 maps to MIPI CAM/DISP0 using sda=38,scl=39.
• The i2c4 maps to MIPI CAM/DISP1 using sda=40,scl=41.

So if someone tries to use a MIPI camera, it will conflict:

BlueOS/install/boards/bcm_2712.sh

Line 58 in bfbe43a

"dtoverlay=i2c-gpio,i2c_gpio_sda=22,i2c_gpio_scl=23,bus=6,i2c_gpio_delay_us=0" \

..and i2c4 is symlinked to i2c3:

BlueOS/core/tools/blueos_startup_update/blueos_startup_update.py

Lines 277 to 287 in bfbe43a

	def update_i2c4_symlink() -> bool:
	logger.info("Running i2c4 symlink update..")
	i2c4_symlink = "/dev/i2c-4"
	i2c4_device = "/dev/i2c-3"
	if os.path.exists(i2c4_symlink):
	return False
	if not os.path.exists(i2c4_device):
	return False
	command = f"sudo ln -s {i2c4_device} {i2c4_symlink}"
	run_command(command, False)
	return False # This patch doesn't require restart to take effect

---

What can we do about it?

For my testing, I moved the i2c-gpio from bus=6 to bus=8:

- "dtoverlay=i2c-gpio,i2c_gpio_sda=22,i2c_gpio_scl=23,bus=6,i2c_gpio_delay_us=0" \
+ "dtoverlay=i2c-gpio,i2c_gpio_sda=22,i2c_gpio_scl=23,bus=8,i2c_gpio_delay_us=0" \

The navigator seemed to be working fine, but there might be side effects.

[ES-Alexander]

The navigator seemed to be working fine, but there might be side effects.

If I'm understanding correctly, I²C 6 is normally used as the external port (e.g. for water barometers and temperature sensors and the like). Have you tested with an external sensor to see if it's still detected after the port reconfiguration?

That aside, if this is an unresolvable issue due to hardware, could the feature be optional instead (like the current legacy camera support)? There are likely people not using a Navigator who still want to connect a camera to that port :-)

[joaoantoniocardoso]

The navigator seemed to be working fine, but there might be side effects.

If I'm understanding correctly, I2C 6 is normally used as the external port (e.g. for water barometers and temperature sensors and the like). Have you tested with an external sensor to see if it's still detected after the port reconfiguration?

Yeah, if the Navigator "I2C 6" is all wired to the Pi "I2C 6" pins, which are the same ones used by the CSI, then no, they probably won't work together...

That aside, if this is an unresolvable issue due to hardware, could the feature be optional instead (like the current legacy camera support)? There are likely people not using a Navigator who still want to connect a camera to that port :-)

Agreed. It'd be a I2C 6 config: sensor or camera.