i.MX6 Solo: maxcpus=1 vs. nosmp: Warning from smp_twd.c?

[Fabio Estevam]

Hi Dirk,

On Thu, Feb 14, 2013 at 12:10 PM, Dirk Behme <dirk.behme at de.bosch.com> wrote:
> Hi,
>
> working on a i.MX6 Solo SoC (one Cortex A9 core) we are usually booting with
> maxcpus=1 a kernel built with CONFIG_NR_CPUS=4. This is done to be able to
> boot the same kernel on the Solo and Quad version of that SoC.
>
> Now, we tried to switch from 'maxcpus=1' to 'nosmp'. With 'nosmp' we get the
> warning [1] in the boot messages. This isn't there with 'maxcpus=1'.

maxcpus=1 and nosmp are not equivalent as per the comment from kernel/smp.c:

/*
 * Setup routine for controlling SMP activation
 *
 * Command-line option of "nosmp" or "maxcpus=0" will disable SMP
 * activation entirely (the MPS table probe still happens, though).
 *
 * Command-line option of "maxcpus=<NUM>", where <NUM> is an integer
 * greater than 0, limits the maximum number of CPUs activated in
 * SMP mode to <NUM>.
 */

void __weak arch_disable_smp_support(void) { }