On Fri, Jan 29, 2021 at 07:29:31PM +0100, Jan Henrik Weinstock wrote:
> This patch proposes to use the device tree to determine the present cpus
> instead of assuming all CONFIG_NRCPUS are actually present in the system.
>
> Signed-off-by: Jan Henrik Weinstock <jan.weinst...@rwth-aachen.de>
> ---
> arch/openrisc/kernel/smp.c | 18 +++++++++++++++---
> 1 file changed, 15 insertions(+), 3 deletions(-)
>
> diff --git a/arch/openrisc/kernel/smp.c b/arch/openrisc/kernel/smp.c
> index 29c82ef2e..75be7e34f 100644
> --- a/arch/openrisc/kernel/smp.c
> +++ b/arch/openrisc/kernel/smp.c
> @@ -16,6 +16,7 @@
> #include <linux/sched.h>
> #include <linux/sched/mm.h>
> #include <linux/irq.h>
> +#include <linux/of.h>
> #include <asm/cpuinfo.h>
> #include <asm/mmu_context.h>
> #include <asm/tlbflush.h>
> @@ -68,14 +69,25 @@ void __init smp_init_cpus(void)
>
> void __init smp_prepare_cpus(unsigned int max_cpus)
> {
> - int i;
> + u32 cpu_id;
> + struct device_node *cpu, *cpus;
>
> /*
> * 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);
> + cpus = of_find_node_by_path("/cpus");
> + for_each_child_of_node(cpus, cpu) {
> + if (of_property_read_u32(cpu, "reg", &cpu_id)) {
> + pr_warn("%s missing reg property", cpu->full_name);
> + continue;
> + }
> +
> + if (cpu_id >= max_cpus)
> + continue;
> +
> + set_cpu_present(cpu_id, true);
> + }
Hello, I looked into what other architectures do. Risc-V does something similar
but it does the setup in 2 parts:
- it uses the device tree to set possible CPU's in setup_smp. Using
for_each_of_cpu_node and set_cpu_possible.
- Then in smp_prepare_cpus, it loops over possible cpus with
for_each_possible_cpu.
Note, it seems risc-v does't actually check max_cpus when setting
set_cpu_present which may be a bug.
I think the two part approach is what we want to do:
- we should do set_cpu_possible in smp_init_cpus based on device tree.
Basically the same as your loop above but using for_each_of_cpu_node
and NR_CPUS.
- we can then do set_cpu_present using for_each_possible_cpu in
smp_prepare_cpus.
What do you think?
-Stafford
> }
>
> void __init smp_cpus_done(unsigned int max_cpus)
> --
> 2.17.1
>
