how to modify the default Linux kernel boot options?

How to modify the default Linux kernel boot options?

As I see from /proc/cmdline on my CARMA/CUDA devboard from SECO, the default command options are
console=ttyS0,115200n8 console=tty1 lp0_vec=0x00002000@0x9C406000 video=tegrafb vmalloc=256M mem=2047M@2048M noinitrd usbcore.old_scheme_first=1 core_edp_mv=1300 panel=lvds tegraid=30.1.2.0.0 debug_uartport=lsport,2 smp tegra_fbmem=3072K@0xBFE00000 max_cpu_cur_ma=10000 root=/dev/mmcblk0p1 rw rootwait gpt

I would like to add to the above options something like ‘maxcpus=2’ or ‘isolcpus=2,3’

I presume it may require interruption of the booting process on the console port (over the
serial port) but don’t want to risk making system unbootable by improper changes.

Where can I find the suitable documentation?

Thanks!

Well, I have figured it out.
The basic concept looks like follows (it is about the CARMA/CUDA board from SECO):

  • establish a console connection over the serial port (115200 8N1, no HW Flow Control)
  • on power-on interrupt the boot process to get to the ‘Tegra3-Seco #’ prompt
  • modify the ‘extra_bootargs’ environment variable
  • continue with the ‘boot’ command

The above ‘extra_bootargs’ modification is for the one booting session, unless the
saveenv command would be used. In other words, the next booting session will use
the original ‘extra_bootargs’ variable content.

Interestingly, the ‘maxcpus=2’ extra boot option does not have any effect.
Looks like the used kernel is modified to utilize all available CPUs.
But the ‘isolcpus=2,3’ works OK, and the CPU2+CPU3 will be ignored by scheduler.

-zenon

Hello Zenon,

It sounds like you are using u-boot, if you look in the Linux For Tegra driver release (https://developer.nvidia.com/linux-tegra), you will see *.hush files in the bootloader folder which can be changed to modify the linux kernel boot options. Once you flash the device with the new bootloader and hush file, you will not need to modify the args from the u-boot command prompt as you are doing above, though that method should also work.

Thanks,
Linux for Tegra
NVIDIA Corporation
2701 San Tomas Expr
Santa Clara, CA 95055