[Qemu-devel] [PATCH v2] riscv: virt: Add cpu-topology DT node.

[Atish Patra <atish.patra@wdc.com>]

Currently, there is no cpu topology defined in RISC-V.
Define a device tree node that clearly describes the
entire topology. This saves the trouble of scanning individual
cache to figure out the topology.

Here is the linux kernel patch series that enables topology
for RISC-V.

http://lists.infradead.org/pipermail/linux-riscv/2019-June/005072.html

CPU topology after applying this patch in QEMU & above series in kernel

/ # cat /sys/devices/system/cpu/cpu2/topology/thread_siblings_list
2
/ # cat /sys/devices/system/cpu/cpu2/topology/physical_package_id
0
/ # cat /sys/devices/system/cpu/cpu2/topology/core_siblings_list
0-7

Signed-off-by: Atish Patra <atish.patra@wdc.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
---
 hw/riscv/virt.c | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/hw/riscv/virt.c b/hw/riscv/virt.c
index 84d94d0c42d8..45a1edcd6c4a 100644
--- a/hw/riscv/virt.c
+++ b/hw/riscv/virt.c
@@ -191,6 +191,7 @@ static void *create_fdt(RISCVVirtState *s, const struct MemmapEntry *memmap,
 
     for (cpu = s->soc.num_harts - 1; cpu >= 0; cpu--) {
         int cpu_phandle = phandle++;
+        int intc_phandle;
         nodename = g_strdup_printf("/cpus/cpu@%d", cpu);
         char *intc = g_strdup_printf("/cpus/cpu@%d/interrupt-controller", cpu);
         char *isa = riscv_isa_string(&s->soc.harts[cpu]);
@@ -203,9 +204,12 @@ static void *create_fdt(RISCVVirtState *s, const struct MemmapEntry *memmap,
         qemu_fdt_setprop_string(fdt, nodename, "status", "okay");
         qemu_fdt_setprop_cell(fdt, nodename, "reg", cpu);
         qemu_fdt_setprop_string(fdt, nodename, "device_type", "cpu");
+        qemu_fdt_setprop_cell(fdt, nodename, "phandle", cpu_phandle);
+        qemu_fdt_setprop_cell(fdt, nodename, "linux,phandle", cpu_phandle);
+        intc_phandle = phandle++;
         qemu_fdt_add_subnode(fdt, intc);
-        qemu_fdt_setprop_cell(fdt, intc, "phandle", cpu_phandle);
-        qemu_fdt_setprop_cell(fdt, intc, "linux,phandle", cpu_phandle);
+        qemu_fdt_setprop_cell(fdt, intc, "phandle", intc_phandle);
+        qemu_fdt_setprop_cell(fdt, intc, "linux,phandle", intc_phandle);
         qemu_fdt_setprop_string(fdt, intc, "compatible", "riscv,cpu-intc");
         qemu_fdt_setprop(fdt, intc, "interrupt-controller", NULL, 0);
         qemu_fdt_setprop_cell(fdt, intc, "#interrupt-cells", 1);
@@ -214,6 +218,20 @@ static void *create_fdt(RISCVVirtState *s, const struct MemmapEntry *memmap,
         g_free(nodename);
     }
 
+    /* Add cpu-topology node */
+    qemu_fdt_add_subnode(fdt, "/cpus/cpu-map");
+    qemu_fdt_add_subnode(fdt, "/cpus/cpu-map/cluster0");
+    for (cpu = s->soc.num_harts - 1; cpu >= 0; cpu--) {
+        char *core_nodename = g_strdup_printf("/cpus/cpu-map/cluster0/core%d",
+                                              cpu);
+        char *cpu_nodename = g_strdup_printf("/cpus/cpu@%d", cpu);
+        uint32_t intc_phandle = qemu_fdt_get_phandle(fdt, cpu_nodename);
+        qemu_fdt_add_subnode(fdt, core_nodename);
+        qemu_fdt_setprop_cell(fdt, core_nodename, "cpu", intc_phandle);
+        g_free(core_nodename);
+        g_free(cpu_nodename);
+    }
+
     cells =  g_new0(uint32_t, s->soc.num_harts * 4);
     for (cpu = 0; cpu < s->soc.num_harts; cpu++) {
         nodename =
-- 
2.21.0