[RFC,v4,5/7] hw/arm/virt: Add cpu-map to device tree

Commit Message

Yanan Wang June 22, 2021, 9:34 a.m. UTC

From: Andrew Jones <[e-mail]>

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 have already met the requirement by generating
/cpus/cpu@* nodes for members within ms->smp.cpus. Accordingly,
we should also create subnodes in cpu-map for the present cpus,
each of which relates to an unique cpu node.

The Linux Doc "cpu/cpu-topology.txt" states that the hierarchy
of CPUs in a SMP system is defined through four entities and
they are socket/cluster/core/thread. It is also required that
a socket node's child nodes must be one or more cluster nodes.
Given that currently we are only provided with information of
socket/core/thread, we assume there is one cluster child node
in each socket node when creating cpu-map.

Signed-off-by: Andrew Jones <[e-mail]>
Co-developed-by: Yanan Wang <[e-mail]>
Signed-off-by: Yanan Wang <[e-mail]>
---
 hw/arm/virt.c | 58 ++++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 48 insertions(+), 10 deletions(-)

Patch

diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index f29d796f3f..645ce7d260 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -355,17 +355,17 @@  static void fdt_add_cpu_nodes(const VirtMachineState *vms)
     int smp_cpus = ms->smp.cpus;
 
     /*
-     * From Documentation/devicetree/bindings/arm/cpus.txt
-     *  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
-     *  in the system, #address-cells can be set to 1, since
-     *  MPIDR_EL1[63:32] bits are not used for CPUs
-     *  identification.
+     * 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
+     * in the system, #address-cells can be set to 1, since
+     * MPIDR_EL1[63:32] bits are not used for CPUs
+     * identification.
      *
-     *  Here we actually don't know whether our system is 32- or 64-bit one.
-     *  The simplest way to go is to examine affinity IDs of all our CPUs. If
-     *  at least one of them has Aff3 populated, we set #address-cells to 2.
+     * Here we actually don't know whether our system is 32- or 64-bit one.
+     * The simplest way to go is to examine affinity IDs of all our CPUs. If
+     * at least one of them has Aff3 populated, we set #address-cells to 2.
      */
     for (cpu = 0; cpu < smp_cpus; cpu++) {
         ARMCPU *armcpu = ARM_CPU(qemu_get_cpu(cpu));
@@ -408,8 +408,46 @@  static void fdt_add_cpu_nodes(const VirtMachineState *vms)
                 ms->possible_cpus->cpus[cs->cpu_index].props.node_id);
         }
 
+        if (ms->expose_cpu_topology) {
+            qemu_fdt_setprop_cell(ms->fdt, nodename, "phandle",
+                                  qemu_fdt_alloc_phandle(ms->fdt));
+        }
+
         g_free(nodename);
     }
+
+    if (ms->expose_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 = 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/cluster0/%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/cluster0/%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)