Re: [RFC PATCH v2 2/6] hw/arm/virt: DT: Add cpu-map

[Andrew Jones <drjones@redhat.com>]

On Tue, Apr 13, 2021 at 04:07:41PM +0800, Yanan Wang wrote:
> From: Andrew Jones <drjones@redhat.com>
> 
> Support device tree CPU topology descriptions.
> 
> Signed-off-by: Andrew Jones <drjones@redhat.com>
> Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
> ---
>  hw/arm/virt.c         | 41 ++++++++++++++++++++++++++++++++++++++++-
>  include/hw/arm/virt.h |  1 +
>  2 files changed, 41 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> index 9f01d9041b..f4ae60ded9 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -352,10 +352,11 @@ static void fdt_add_cpu_nodes(const VirtMachineState *vms)
>      int cpu;
>      int addr_cells = 1;
>      const MachineState *ms = MACHINE(vms);
> +    const VirtMachineClass *vmc = VIRT_MACHINE_GET_CLASS(vms);
>      int smp_cpus = ms->smp.cpus;
>  
>      /*
> -     * From Documentation/devicetree/bindings/arm/cpus.txt
> +     *  See Linux Documentation/devicetree/bindings/arm/cpus.yaml
>       *  On ARM v8 64-bit systems value should be set to 2,
>       *  that corresponds to the MPIDR_EL1 register size.
>       *  If MPIDR_EL1[63:32] value is equal to 0 on all CPUs
> @@ -408,8 +409,45 @@ static void fdt_add_cpu_nodes(const VirtMachineState *vms)
>                  ms->possible_cpus->cpus[cs->cpu_index].props.node_id);
>          }
>  
> +        if (ms->smp.cpus > 1 && !vmc->no_cpu_topology) {

We should probably always generate the cpu-map, like we agreed to always
generate the PPTT. If, for some reason, we don't want to generate the
cpu-map for uniprocessor systems, then we should actually be checking
ms->smp.maxcpus here (and below) to be sure it's uniprocessor.

Thanks,
drew

> +            qemu_fdt_setprop_cell(ms->fdt, nodename, "phandle",
> +                                  qemu_fdt_alloc_phandle(ms->fdt));
> +        }
> +
>          g_free(nodename);
>      }
> +
> +    if (ms->smp.cpus > 1 && !vmc->no_cpu_topology) {
> +        /*
> +         * See Linux Documentation/devicetree/bindings/cpu/cpu-topology.txt
> +         * In a SMP system, the hierarchy of CPUs is defined through four
> +         * entities that are used to describe the layout of physical CPUs
> +         * in the system: socket/cluster/core/thread.
> +         */
> +        qemu_fdt_add_subnode(ms->fdt, "/cpus/cpu-map");
> +
> +        for (cpu = ms->smp.cpus - 1; cpu >= 0; cpu--) {
> +            char *cpu_path = g_strdup_printf("/cpus/cpu@%d", cpu);
> +            char *map_path;
> +
> +            if (ms->smp.threads > 1) {
> +                map_path = g_strdup_printf(
> +                    "/cpus/cpu-map/%s%d/%s%d/%s%d",
> +                    "socket", cpu / (ms->smp.cores * ms->smp.threads),
> +                    "core", (cpu / ms->smp.threads) % ms->smp.cores,
> +                    "thread", cpu % ms->smp.threads);
> +            } else {
> +                map_path = g_strdup_printf(
> +                    "/cpus/cpu-map/%s%d/%s%d",
> +                    "socket", cpu / ms->smp.cores,
> +                    "core", cpu % ms->smp.cores);
> +            }
> +            qemu_fdt_add_path(ms->fdt, map_path);
> +            qemu_fdt_setprop_phandle(ms->fdt, map_path, "cpu", cpu_path);
> +            g_free(map_path);
> +            g_free(cpu_path);
> +        }
> +    }
>  }
>  
>  static void fdt_add_its_gic_node(VirtMachineState *vms)
> @@ -2769,6 +2807,7 @@ static void virt_machine_5_2_options(MachineClass *mc)
>      virt_machine_6_0_options(mc);
>      compat_props_add(mc->compat_props, hw_compat_5_2, hw_compat_5_2_len);
>      vmc->no_secure_gpio = true;
> +    vmc->no_cpu_topology = true;
>  }
>  DEFINE_VIRT_MACHINE(5, 2)
>  
> diff --git a/include/hw/arm/virt.h b/include/hw/arm/virt.h
> index 921416f918..4a4b98e4a7 100644
> --- a/include/hw/arm/virt.h
> +++ b/include/hw/arm/virt.h
> @@ -129,6 +129,7 @@ struct VirtMachineClass {
>      bool no_kvm_steal_time;
>      bool acpi_expose_flash;
>      bool no_secure_gpio;
> +    bool no_cpu_topology;
>  };
>  
>  struct VirtMachineState {
> -- 
> 2.19.1
>