Hello, i manage to flash openwrt on this router and i can do reboot with no problem, but if i poweroff the router for a few minutes, when i turn on it returns to Linksys firmware.
How can i flash openwrt on both partitions or fix this "problem"?
Wiki states that Openwrt is only running on partition 1.
Have a look to the EA7300 v2 documentation and check if the S_ENV behavior if the same. Several devices do so (EA7500v2), but I can't tell for V3 (it's not even the same target).
This tweak works on the EA7300v2. It worked also on the EA7500v2 because there are in the same target, and probably use the same bootloader software. EA7500v3 is not in the same target. I guess you have to find another way. Monitor the boot process with serial, and watch u-boot variables.
The general behavior of switching partition is a deliberate choice of the manufactor and is implemented in the bootloader. Goal is to force switching partition if the current one is corrupted in some way, and to land on a valid partition.