Linux i2c mapping
rreignier
New Member Posts: 67 ✭✭
Does some know the mapping of the i2c buses on Linux.
/sys/bus/i2c/devices/ shows 10 i2c buses:
$ ls -l /sys/bus/i2c/devices/ total 0 lrwxrwxrwx 1 root root 0 Jan 20 17:33 i2c-0 -> ../../../devices/pci0000:00/0000:00:16.0/i2c_designware.0/i2c-0 lrwxrwxrwx 1 root root 0 Jan 20 17:33 i2c-1 -> ../../../devices/pci0000:00/0000:00:16.1/i2c_designware.1/i2c-1 lrwxrwxrwx 1 root root 0 Jan 20 17:33 i2c-2 -> ../../../devices/pci0000:00/0000:00:17.0/i2c_designware.2/i2c-2 lrwxrwxrwx 1 root root 0 Jan 20 17:33 i2c-3 -> ../../../devices/pci0000:00/0000:00:02.0/i2c-3 lrwxrwxrwx 1 root root 0 Jan 20 17:33 i2c-4 -> ../../../devices/pci0000:00/0000:00:02.0/i2c-4 lrwxrwxrwx 1 root root 0 Jan 20 17:33 i2c-5 -> ../../../devices/pci0000:00/0000:00:02.0/i2c-5 lrwxrwxrwx 1 root root 0 Jan 20 17:33 i2c-6 -> ../../../devices/pci0000:00/0000:00:02.0/drm/card0/card0-DP-1/i2c-6 lrwxrwxrwx 1 root root 0 Jan 20 17:33 i2c-7 -> ../../../devices/pci0000:00/0000:00:02.0/drm/card0/card0-DP-2/i2c-7 lrwxrwxrwx 1 root root 0 Jan 20 17:33 i2c-8 -> ../../../devices/pci0000:00/0000:00:17.2/i2c_designware.3/i2c-8 lrwxrwxrwx 1 root root 0 Jan 20 17:33 i2c-9 -> ../../../devices/pci0000:00/0000:00:17.3/i2c_designware.4/i2c-9
The 100-pin connector has I2C0, I2C1 and I2C6. But what are their mapping to Linux buses?
Thanks you.
Comments
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Actually, the mapping seem to change upon reboot.
I have an IMU connected to I2C-1 on 100 pin connector.
After a cold boot I have:user@upcoreplus:~/scripts$ i2cdetect -r -y 6 0 1 2 3 4 5 6 7 8 9 a b c d e f 00: -- -- -- -- -- -- -- -- -- -- -- -- -- 10: -- -- -- -- -- -- -- -- -- -- -- -- 1c -- -- -- 20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 60: -- -- -- -- -- -- -- -- -- -- 6a -- -- -- -- -- 70: -- -- -- -- -- -- -- -- user@upcoreplus:~/scripts$ ls -l /sys/class/i2c-adapter/ total 0 lrwxrwxrwx 1 root root 0 Mar 6 18:17 i2c-0 -> ../../devices/pci0000:00/0000:00:02.0/i2c-0 lrwxrwxrwx 1 root root 0 Mar 6 18:17 i2c-1 -> ../../devices/pci0000:00/0000:00:02.0/i2c-1 lrwxrwxrwx 1 root root 0 Mar 6 18:17 i2c-2 -> ../../devices/pci0000:00/0000:00:02.0/i2c-2 lrwxrwxrwx 1 root root 0 Mar 6 18:17 i2c-3 -> ../../devices/pci0000:00/0000:00:02.0/drm/card0/card0-DP-1/i2c-3 lrwxrwxrwx 1 root root 0 Mar 6 18:17 i2c-4 -> ../../devices/pci0000:00/0000:00:02.0/drm/card0/card0-DP-2/i2c-4 lrwxrwxrwx 1 root root 0 Mar 6 18:17 i2c-5 -> ../../devices/pci0000:00/0000:00:16.0/i2c_designware.0/i2c-5 lrwxrwxrwx 1 root root 0 Mar 6 18:17 i2c-6 -> ../../devices/pci0000:00/0000:00:16.1/i2c_designware.1/i2c-6 lrwxrwxrwx 1 root root 0 Mar 6 18:17 i2c-7 -> ../../devices/pci0000:00/0000:00:17.0/i2c_designware.2/i2c-7 lrwxrwxrwx 1 root root 0 Mar 6 18:17 i2c-8 -> ../../devices/pci0000:00/0000:00:17.2/i2c_designware.3/i2c-8 lrwxrwxrwx 1 root root 0 Mar 6 18:17 i2c-9 -> ../../devices/pci0000:00/0000:00:17.3/i2c_designware.4/i2c-9After a reboot:
user@upcoreplus:~$ i2cdetect -r -y 6 0 1 2 3 4 5 6 7 8 9 a b c d e f 00: -- -- -- -- -- -- -- -- -- -- -- -- -- 10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 70: -- -- -- -- -- -- -- -- user@upcoreplus:~$ i2cdetect -r -y 1 0 1 2 3 4 5 6 7 8 9 a b c d e f 00: -- -- -- -- -- -- -- -- -- -- -- -- -- 10: -- -- -- -- -- -- -- -- -- -- -- -- 1c -- -- -- 20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 60: -- -- -- -- -- -- -- -- -- -- 6a -- -- -- -- -- 70: -- -- -- -- -- -- -- -- user@upcoreplus:~$ ls -l /sys/class/i2c-adapter/ total 0 lrwxrwxrwx 1 root root 0 Mar 6 18:38 i2c-0 -> ../../devices/pci0000:00/0000:00:16.0/i2c_designware.0/i2c-0 lrwxrwxrwx 1 root root 0 Mar 6 18:38 i2c-1 -> ../../devices/pci0000:00/0000:00:16.1/i2c_designware.1/i2c-1 lrwxrwxrwx 1 root root 0 Mar 6 18:38 i2c-2 -> ../../devices/pci0000:00/0000:00:17.0/i2c_designware.2/i2c-2 lrwxrwxrwx 1 root root 0 Mar 6 18:38 i2c-3 -> ../../devices/pci0000:00/0000:00:17.2/i2c_designware.3/i2c-3 lrwxrwxrwx 1 root root 0 Mar 6 18:38 i2c-4 -> ../../devices/pci0000:00/0000:00:17.3/i2c_designware.4/i2c-4 lrwxrwxrwx 1 root root 0 Mar 6 18:38 i2c-5 -> ../../devices/pci0000:00/0000:00:02.0/i2c-5 lrwxrwxrwx 1 root root 0 Mar 6 18:38 i2c-6 -> ../../devices/pci0000:00/0000:00:02.0/i2c-6 lrwxrwxrwx 1 root root 0 Mar 6 18:38 i2c-7 -> ../../devices/pci0000:00/0000:00:02.0/i2c-7 lrwxrwxrwx 1 root root 0 Mar 6 18:38 i2c-8 -> ../../devices/pci0000:00/0000:00:02.0/drm/card0/card0-DP-1/i2c-8 lrwxrwxrwx 1 root root 0 Mar 6 18:38 i2c-9 -> ../../devices/pci0000:00/0000:00:02.0/drm/card0/card0-DP-2/i2c-9So the i2c assignment is not predictable. Do you have any workaround?
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From Kernel documentation: https://www.kernel.org/doc/Documentation/i2c/dev-interface
"Now, you have to decide which adapter you want to access. You should
inspect /sys/class/i2c-dev/ or run "i2cdetect -l" to decide this.
Adapter numbers are assigned somewhat dynamically, so you can not
assume much about them. They can even change from one boot to the next." -
Thank you @DCleri
I have ended up with this small script to determine the i2c interface on boot:
pushd /sys/devices/pci0000\:00/0000\:00\:16.1/i2c_designware.1/ > /dev/null I2CDEV=$(ls -1 | grep "i2c-") echo "IMU on $I2CDEV" popd > /dev/null
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I am glad that you have found that solution, I am sure it can be helpful to other people too.
