[RFC 1/4] riscv: arch-topology: fix default topology reporting

[Conor Dooley]

From: Conor Dooley <conor.dooley at microchip.com>

RISC-V has no sane defaults to fall back on where there is no cpu-map
in the devicetree.
Without sane defaults, the package, core and thread IDs are all set to
-1. This causes user-visible inaccuracies for tools like hwloc/lstopo
which rely on the sysfs cpu topology files to detect a system's
topology.

Add sane defaults in ~the exact same way as ARM64.

CC: stable at vger.kernel.org
Fixes: 03f11f03dbfe ("RISC-V: Parse cpu topology during boot.")
Reported-by: Brice Goglin <Brice.Goglin at inria.fr>
Link: https://github.com/open-mpi/hwloc/issues/536
Signed-off-by: Conor Dooley <conor.dooley at microchip.com>
---
Sudeep suggested that this be backported rather than the changes to
the devicetrees adding cpu-map since that property is optional.
That patchset is still valid in it's own right.

Changes since v1:
- removed the GENERIC_ARCH_TOPOLOGY dependancy on SMP
- removed a duplicate call to update_siblings_masks()
---
 arch/riscv/Kconfig                |  2 +-
 arch/riscv/include/asm/topology.h | 13 +++++++++++++
 arch/riscv/kernel/Makefile        |  1 +
 arch/riscv/kernel/smpboot.c       |  5 ++++-
 arch/riscv/kernel/topology.c      | 32 +++++++++++++++++++++++++++++++
 5 files changed, 51 insertions(+), 2 deletions(-)
 create mode 100644 arch/riscv/include/asm/topology.h
 create mode 100644 arch/riscv/kernel/topology.c

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 2af0701b7518..4b6c2fdbb57c 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -52,7 +52,7 @@ config RISCV
 	select COMMON_CLK
 	select CPU_PM if CPU_IDLE
 	select EDAC_SUPPORT
-	select GENERIC_ARCH_TOPOLOGY if SMP
+	select GENERIC_ARCH_TOPOLOGY
 	select GENERIC_ATOMIC64 if !64BIT
 	select GENERIC_CLOCKEVENTS_BROADCAST if SMP
 	select GENERIC_EARLY_IOREMAP
diff --git a/arch/riscv/include/asm/topology.h b/arch/riscv/include/asm/topology.h
new file mode 100644
index 000000000000..36bc6ecda898
--- /dev/null
+++ b/arch/riscv/include/asm/topology.h
@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (c) 2022 Microchip Technology Inc. and its subsidiaries
+ */
+
+#ifndef _ASM_RISCV_TOPOLOGY_H
+#define _ASM_RISCV_TOPOLOGY_H
+
+#include <asm-generic/topology.h>
+
+void store_cpu_topology(unsigned int cpuid);
+
+#endif /* _ASM_RISCV_TOPOLOGY_H */
diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index c71d6591d539..9518882ba6f9 100644
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile
@@ -50,6 +50,7 @@ obj-y	+= riscv_ksyms.o
 obj-y	+= stacktrace.o
 obj-y	+= cacheinfo.o
 obj-y	+= patch.o
+obj-y	+= topology.o
 obj-y	+= probes/
 obj-$(CONFIG_MMU) += vdso.o vdso/
 
diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
index f1e4948a4b52..a8239b4b61f3 100644
--- a/arch/riscv/kernel/smpboot.c
+++ b/arch/riscv/kernel/smpboot.c
@@ -32,6 +32,7 @@
 #include <asm/sections.h>
 #include <asm/sbi.h>
 #include <asm/smp.h>
+#include <asm/topology.h>
 
 #include "head.h"
 
@@ -40,6 +41,8 @@ static DECLARE_COMPLETION(cpu_running);
 void __init smp_prepare_boot_cpu(void)
 {
 	init_cpu_topology();
+
+	store_cpu_topology(smp_processor_id());
 }
 
 void __init smp_prepare_cpus(unsigned int max_cpus)
@@ -161,9 +164,9 @@ asmlinkage __visible void smp_callin(void)
 	mmgrab(mm);
 	current->active_mm = mm;
 
+	store_cpu_topology(curr_cpuid);
 	notify_cpu_starting(curr_cpuid);
 	numa_add_cpu(curr_cpuid);
-	update_siblings_masks(curr_cpuid);
 	set_cpu_online(curr_cpuid, 1);
 
 	/*
diff --git a/arch/riscv/kernel/topology.c b/arch/riscv/kernel/topology.c
new file mode 100644
index 000000000000..db72862bd5b5
--- /dev/null
+++ b/arch/riscv/kernel/topology.c
@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2022 Microchip Technology Inc. and its subsidiaries
+ *
+ * Based on the arm64 version, which was in turn based on arm32, which was
+ * ultimately based on sh's.
+ * The arm64 version was listed as:
+ * Copyright (C) 2011,2013,2014 Linaro Limited.
+ */
+
+#include <linux/arch_topology.h>
+#include <linux/topology.h>
+#include <asm/topology.h>
+
+void store_cpu_topology(unsigned int cpuid)
+{
+	struct cpu_topology *cpuid_topo = &cpu_topology[cpuid];
+
+	if (cpuid_topo->package_id != -1)
+		goto topology_populated;
+
+	cpuid_topo->thread_id = -1;
+	cpuid_topo->core_id = cpuid;
+	cpuid_topo->package_id = cpu_to_node(cpuid);
+
+	pr_debug("CPU%u: package %d core %d thread %d\n",
+		 cpuid, cpuid_topo->package_id, cpuid_topo->core_id,
+		 cpuid_topo->thread_id);
+
+topology_populated:
+	update_siblings_masks(cpuid);
+}
-- 
2.37.0