Re: [RFC PATCH v3 3/9] hw/arm/virt: Add cpu-map to device tree

[Andrew Jones <drjones@redhat.com>]

On Sun, May 16, 2021 at 06:28:54PM +0800, Yanan Wang wrote:
> From: Andrew Jones <drjones@redhat.com>
> 
> Support device tree CPU topology descriptions.
> 
> In accordance with the Devicetree Specification, the Linux Doc
> "arm/cpus.yaml" requires that cpus and cpu nodes in the DT are
> present. And we meet the requirement by creating /cpus/cpu@*
> nodes for members within ms->smp.cpus.
> 
> Correspondingly, we should also create subnodes in cpu-map for
> the present cpus, each of which relates to an unique cpu node.
> 
> Signed-off-by: Andrew Jones <drjones@redhat.com>
> Co-developed-by: Yanan Wang <wangyanan55@huawei.com>
> Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
> ---
>  hw/arm/virt.c | 41 ++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 40 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> index c07841e3a4..e5dcdebdbc 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -349,10 +349,11 @@ 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

Rather than aligning the top line with the lower lines, we could remove
the extra space from the lower lines. Or, leave the formatting as it was,
by putting 'See' where 'From' was, like I did in my original patch.

>       *  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
> @@ -405,8 +406,46 @@ static void fdt_add_cpu_nodes(const VirtMachineState *vms)
>                  ms->possible_cpus->cpus[cs->cpu_index].props.node_id);
>          }
>  
> +        if (!vmc->no_cpu_topology) {
> +            qemu_fdt_setprop_cell(ms->fdt, nodename, "phandle",
> +                                  qemu_fdt_alloc_phandle(ms->fdt));
> +        }
> +
>          g_free(nodename);
>      }
> +
> +    if (!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

s/entities/levels/

> +         * in the system: socket/cluster/core/thread.

The comment says there are four levels including 'cluster', but there's no
'cluster' below.

> +         */
> +        qemu_fdt_add_subnode(ms->fdt, "/cpus/cpu-map");
> +
> +        for (cpu = 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)
> -- 
> 2.19.1
>

Thanks,
drew