where does default setting for Command Line Switches is set in kernel source code in android My android device is quad-core . But during booting only 2 cores are up . CPU_HOTPLUG is enabled . In dumpstate i found :

maxcpus=2 

in command Line options.
I wanted to make this maxcpus=4 . I have all source code with me . I wanted to set this maxcpus value in source code (especially in default settings) .

So my question is : In which file does this default value setting is done ? I grep'ed it through source in platform and kernel. But i didn't get any clue .I think this code lie in bootloader .If so please guide me
I presume that CPU_HOTPLUG means hotplug cpu governor is enabled in your system.
hotplug cpu governor can make cpu core online or offline based on total system load.
So, It might be possible that your other two cores are offline at the moment.

You can check the exact cpu cores by,

$ cat /sys/devices/system/cpu/present

This will display total cores on your system. Or you can do "ls /sys/devices/system/cpu/cpu*" then see cpu0,cpu1,... directories. Those are your different cores.

If you can not find 4 cores (0,1,2,3) in that directory, than there is some problem with your system.

You can change the cpu governor to some other for example, ondemand to utilize all four cores. But it may use more battery.

I hope this helps.

[update]
Also, if you are referring to set the default kernel command line from configuration then it is available at,

Symbol: CMDLINE [=]

Type  : string 

Prompt: Default kernel command string

Defined at arch/arm/Kconfig:1766

Location:
-> Boot options

in kernel menuconfig window.

Generally in android, kernel commandline is part of boot image and not this default one, But you can still try that out. If bootloader is passing the kernel command line string than this configuration will be ignored.

Good luck.