How do we switch from protected mode to real mode in Linux 2.6?
No.
The kernel cannot function at all in real mode, and BIOS calls cannot be (reasonably) made, so you can’t do anything anyway.
You can see how DosEMU uses v86 mode to run your "real mode" code, but that's all.
You can also take a look at FreeDOS if you really need real mode on the hardware.
The kernel switches from real mode to protected mode at the very beginning of the boot / start sequence and there is no going back. See How boot loaders work for more information.
If you have a program that needs real mode, there is v86 mode . Some work is ongoing to add support for this in 64-bit mode.
ELKS Linux port can work in real mode, but it is nowhere around 2.6.
We can switch from protected mode to real mode by writing some lines of code as part of the kernel.
The main thing is, after the PE bit register in cr0 is disabled, we need to load the corresponding GDT, LDT, IDT . Just follow this link for more information http://www.sudleyplace.com/pmtorm.html .