On 10/26/2016 01:04 AM, Noam Camus wrote:
> From: Noam Camus <noamca at mellanox.com>
>
> Today we use smp_init_cpus() to set cpu possible mask
> and we use smp_prepare_cpus() to set cpu present mask.
> For possible mask we use all CPUs at range [0-NR_CPUS] and
> for present mask we use all CPUs at range [0-max_cpus]
> which is actually the same as possible mask (no hutplug).
>
> For platform like eznps we wish to have more configurable range then
> being statically defined by NR_CPUS (actuall derived from CONFIG_NR_CPUS).
> For this purpose we added two new entries at our device tree root level:
> possible-cpus
> present-cpus
>
> The format of this new entries is same like for all similar kernel
> parameters which provide cpu list (see Documentation/kernel-parameters.txt)
> example of use would be (assume CONFIG_NR_CPUS=8):
> present-cpus = "0-1,6-7";
> possible-cpus = "0-7";
>
> Now if we provide such list in our DT then we won't use the statically range.
> In our example above only CPUs 0,1,6,7 will be up after boot.
>
> Signed-off-by: Noam Camus <noamca at mellanox.com>
> ---
> arch/arc/kernel/smp.c | 32 ++++++++++++++++++++++++++++----
> 1 files changed, 28 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arc/kernel/smp.c b/arch/arc/kernel/smp.c
> index 03d5151..5855403 100644
> --- a/arch/arc/kernel/smp.c
> +++ b/arch/arc/kernel/smp.c
> @@ -16,6 +16,7 @@
> #include <linux/sched.h>
> #include <linux/interrupt.h>
> #include <linux/profile.h>
> +#include <linux/of_fdt.h>
> #include <linux/mm.h>
> #include <linux/cpu.h>
> #include <linux/irq.h>
> @@ -34,6 +35,21 @@ arch_spinlock_t smp_bitops_lock = __ARCH_SPIN_LOCK_UNLOCKED;
>
> struct plat_smp_ops __weak plat_smp_ops;
>
> +/* Get CPUs mask from device tree */
> +static int __init smp_get_cpumask(const char *name, struct cpumask *cpumask)
> +{
> + unsigned long dt_root = of_get_flat_dt_root();
> + const char *buf;
> +
> + buf = of_get_flat_dt_prop(dt_root, name, NULL);
> + if (!buf)
> + return 0;
> +
> + cpulist_parse(buf, cpumask);
> +
> + return 1;
> +}
> +
> /* XXX: per cpu ? Only needed once in early seconday boot */
> struct task_struct *secondary_idle_tsk;
>
> @@ -54,9 +70,13 @@ void __init smp_prepare_boot_cpu(void)
> void __init smp_init_cpus(void)
> {
> unsigned int i;
> + struct cpumask cpumask;
>
> - for (i = 0; i < NR_CPUS; i++)
> - set_cpu_possible(i, true);
> + if (smp_get_cpumask("possible-cpus", &cpumask))
> + init_cpu_possible(&cpumask);
> + else
> + for (i = 0; i < NR_CPUS; i++)
> + set_cpu_possible(i, true);
This is not checkpatch clean, need to enclose the if / else in { }
Anyhow, it seems we don't need this as ARC set_cpu_possible() will be overridden
by your init_early_smp() hook anyways ? We don't need to generalize it as I don't
foresee other platforms needing it.
>
> if (plat_smp_ops.init_early_smp)
> plat_smp_ops.init_early_smp();
> @@ -66,13 +86,17 @@ void __init smp_init_cpus(void)
> void __init smp_prepare_cpus(unsigned int max_cpus)
> {
> int i;
> + struct cpumask cpumask;
>
> /*
> * Initialise the present map, which describes the set of CPUs
> * actually populated at the present time.
> */
> - for (i = 0; i < max_cpus; i++)
> - set_cpu_present(i, true);
> + if (smp_get_cpumask("present-cpus", &cpumask))
> + init_cpu_present(&cpumask);
> + else
> + for (i = 0; i < max_cpus; i++)
> + set_cpu_present(i, true);
> }
With the existing DT based cpu bitmap setting in your platform code, can we
instead do something like below in smp_prepare_cpus():
if (num_present_cpus() <= 1) { /* boot already marked present in init/main.c */
for (i = 0; i < max_cpus; i++)
set_cpu_present(i, true);
}
So to summarize you keep the existing DT based cpu bitmap settings in your
platform code and just add one workaround to not over-ride present map in ARC
common code.
-Vineet
