i.Core MX8MM PMIC software solution
Engicam replaced on i.Core MX8MM SOC the PMIC PF8100 with PCA9450.
In order to manage in the simplest way, the new PMIC mounted on i.Core MX8M mini SOM, we provide a simple software solution that includes a device tree with the new settings and a python3 script that can help the customers easily swap the device tree for the old PMIC with the new one, and vice versa.
The device tree
The supported kernels are:
linux-engicam-nxp (https://github.com/engicam-stable/linux-engicam-nxp) 5.4.70 and 5.10.9 branch
linux-engicam_4.19.35 (https://github.com/engicam-stable/linux-engicam_4.19.35)
linux-engicam_4.14.98 (https://github.com/engicam-stable/linux-engicam_4.14.98)
The idea is to provide a new device tree written to include the customer device tree and replace from it the old pmic settings with the new one.
We provide an example for the starter kit device tree at this link:
As you can see at line 8 we include the old starter kit device tree, based on PF8100 , named imx8mm-icore.dts , and from it replace all PMIC nodes with the new one.
After kernel build we will obtain 2 different device trees for the starter kit:
* imx8mm-icore.dtb (old pmic PF8100)
* imx8mm-icore-pca9450.dtb (new pmic PCA9450)
So you need to change the default device tree load from the system with the right one.
To do this we write a simple python script that checks what PMIC is present on SOM and set the new device tree as the default device tree.
The script must be run during the production phase, not in the field. Read carefully the known issue chapter.
In this example the naming convention user for dtbs is:
<original-dtb-name>.dtb the old one
<original-dtb-name>-pca9450.dtb the new one
basically, the new dtb name is the old one added with postfix -pca9450
The python script
The script uses the tools below:
i2cdetect
fw_setenv
fw_printenv
At the beginning, it checks if these tools exist on the filesystem or not, next, it checks if the script was already run by checking the existence of file /etc/pmic.done, and finally it tests on i2c bus what PMIC is present and if it already probed from the system. If not, it changes the fdt_file u-boot variable with the right device tree using the fw_setenv tools.
The naming convention for the device trees is described in the previous chapter.
The script is on Engicam's github page:
https://github.com/engicam-stable/imx8mm-pmic-fixer-script
known issues
The reboot of the SOM is done by the PMIC using the WDOG_B signal from the SOC. If the PMIC is not properly set by the driver the SOM will stuck in reset condition. This means that a system booted with the wrong device tree is unable to reboot. After DTB settings you must remove the power to the system in order to reboot it.
