I have created my machine to include imx6ullevk.conf to allow me to overwrite some of u-boot parameters over imx6ullevk.conf. In imx6ullevk.conf, I can overwrite u-boot parameter "console" via SERIAL_CONSOLE, but what are names of other macros / parameters in imx6ullevk.conf I could overwrite u-boot mtdparts, bootargs, bootcmd etc in my machine conf file? Is it also possible to create my own u-boot new parameters such as nand-boot, dtbaddr etc?
In general, I would like to see the the what names I could defined to overwrite u-boot source configure file, are there any document to show links between defined macros / parameters and the u-boot configure source so change macros / parameters in machine conf file could easily overwrite or create new parameters during u-boot build?
As per my understanding you want to modify the u-boot environment variable. You can do that by doing changes in the board file of u-boot source, as mentioned by @gusarambula .
Also SERIAL_CONSOLE variable is for changing the baud rate of application's console. It is related to the getty console. You can find the similar variables in Yocto Project Reference Manual, section 14.1.2.
Let us know if you have any further query.
The following thread may be of help:
You can change or add more parameters as needed. Just make sure that the changes are made in a recipe with a high enough priority so that they are reflected on the end image.
I hope this helps!