Printk Behaviour Change with Early_Printk Enabled

It's not really a mapping. When early_printk is enabled, the same printk() is used as before, just new boot console is being registered in that case, and printk() uses it on early boot stages.

Look at arch/arm/kernel/early_printk.c. You can see that:

• new console being registered with register_console() function
• that console has CON_BOOT flag, so it's unregistered automatically as soon as real console is registered
• printing happens via early_write() function, which in turn uses printch() function, which implemented for each platform separately

Where in kernel source the early_console is disabled after kernel console initialization?

It's done in register_console() function:

if (bcon &&
    ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV) &&
    !keep_bootcon) {
        /* We need to iterate through all boot consoles, to make
         * sure we print everything out, before we unregister them.
         */
         for_each_console(bcon)
             if (bcon->flags & CON_BOOT)
                 unregister_console(bcon);
}

All boot consoles are disabled by unregister_console() function in code above (when real console is being registered).

And where is the real console getting registered?

Real consoles use the same method for registration -- register_console() function. For example:

• from my board's defconfig file (arch/arm/configs/omap2plus_defconfig) I can see that my board is using CONFIG_SERIAL_8250 as real console
• we can search where register_console() is executed in my serial driver; it's done in univ8250_console_init() function

Is there any way to keep boot consoles up after console initialization and disable real console?

Boot consoles are automatically unregistered only when real console is registered. Following this logic, you just need to disable the real console in order to keep boot console intact.

So what you need to do, is to find out which exactly driver is used for real console in your case. You can do that looking into your .config file, or the *_defconfig file for your board. Once you located it, just disable that driver in configuration and rebuild the kernel.

If after doing so you keep observing the registering of some real console, you need to add some debug printings to register_console(), to figure out what driver is being registered, and then disable it in your configuration.