How to fix i2c dev/node name mapping

Technical Support
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#1

Hello,

I am working on OpenEmbedded Linux project (Yocto BSP). I am using Apalis iMX8QXP 2GB WB IT - V1.1B.

I am facing an issue regarding I2C dev-node name mapping, please refer to image at below:

2638-i2c.png

I realized that mapping of left and right may not be the same again after re-imaging.

For example, i2c-20 map with 58226000.i2c, and after re-image (via recover mode), and the mapping is different, (i2c-20 map with 56246000.i2c).

I wish to fix the mapping for my image, is it need to do something in device tree ?
Please teach me the method in details. Thanks.

Or any workaround, for example , do mapping manually during my application start ?

#2

Hello @gustavo.tx , @alex.tx ,
Do you have any idea regarding this ?
Or you know anyone good in this ?
Thank you.

#3

Hi

Are your I2C’s listed in DT aliases section?
ls /sys/firmware/devicetree/base/aliases

If not then try enumerating them there.

Edward

#4

Hi @Edward

Thanks for your reply.
Please refer to below:
these are the result after typing :

i2cdetect -l
ls /sys/firmware/devicetree/base/aliases

2648-i2cenum.png
2648-i2cenum.png777×299 9.33 KB

The reason why I wish to make the mapping of dev/node name as a constant, is because during C/C++ coding implementation :
https://www.kernel.org/doc/Documentation/i2c/dev-interface

We use “/dev/i2c-%d” to identify the i2c pin, for example “dev/i2c-20”.

And “dev/i2c-20” is not always map with i258226000.i2c after reimaging, and this cause some problem to me. Please teach me how should I handle this in details, thank you very much !

#5

Devices listed in DT aliases section usually match with /dev/xxxN device numbers. They same with i2cdetect or devices listed in /sys/bus/i2c/devices/.

In device tree imx8qxp.dtsi has this
i2c1 = &i2c_rpbus_1;
i2c5 = &i2c_rpbus_5;
i2c12 = &i2c_rpbus_12;
i2c13 = &i2c_rpbus_13;
i2c14 = &i2c_rpbus_14;
i2c15 = &i2c_rpbus_15;

and your listed devices, which seem to be defined in imx8-ss-dma.dtsi as i2c0, i2c1, i2c2, etc are not referenced from aliases section. That’s why it could be random.

Edward

#6

You are likely looking for something like the following already implemented in BSP 5.x:

https://git.toradex.com/cgit/meta-toradex-bsp-common.git/tree/recipes-core/udev/files/apalis-imx8x/99-toradex.rules?h=dunfell-5.x.y