linux-kernel - [PATCH v2 1/5] x86/topology: Export helper to get CPU number from APIC ID

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Date: Mon, 24 Jun 2024 16:20:04 -0500
From: Yazen Ghannam <yazen.ghannam@....com>
To: <linux-edac@...r.kernel.org>
CC: <linux-kernel@...r.kernel.org>, <tony.luck@...el.com>, <x86@...nel.org>,
	<avadhut.naik@....com>, <john.allen@....com>, Yazen Ghannam
	<yazen.ghannam@....com>
Subject: [PATCH v2 1/5] x86/topology: Export helper to get CPU number from APIC ID

The need to look up a CPU number from an APIC ID is done in at least one
other place outside of APIC/topology code: apei_smca_report_x86_error().

With the recent topology rework, there is now a helper function to do
just this task.

Export the helper so other code can use it. Also, update the name to
match other exported topology_* helpers.

Signed-off-by: Yazen Ghannam <yazen.ghannam@....com>
---
Link:
https://lkml.kernel.org/r/20240618172447.GA1387@yaz-khff2.amd.com

v1->v2:
* New in v2.

 arch/x86/include/asm/topology.h |  6 ++++++
 arch/x86/kernel/cpu/topology.c  | 15 ++++++++++++---
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/topology.h b/arch/x86/include/asm/topology.h
index abe3a8f22cbd..d8c3c3c818bc 100644
--- a/arch/x86/include/asm/topology.h
+++ b/arch/x86/include/asm/topology.h
@@ -171,11 +171,17 @@ static inline unsigned int topology_num_threads_per_package(void)
 
 #ifdef CONFIG_X86_LOCAL_APIC
 int topology_get_logical_id(u32 apicid, enum x86_topology_domains at_level);
+int topology_get_cpunr(u32 apic_id);
 #else
 static inline int topology_get_logical_id(u32 apicid, enum x86_topology_domains at_level)
 {
 	return 0;
 }
+
+static inline int topology_get_cpunr(u32 apic_id)
+{
+	return -ENODEV;
+}
 #endif
 
 #ifdef CONFIG_SMP
diff --git a/arch/x86/kernel/cpu/topology.c b/arch/x86/kernel/cpu/topology.c
index 621a151ccf7d..fc74578ee3bd 100644
--- a/arch/x86/kernel/cpu/topology.c
+++ b/arch/x86/kernel/cpu/topology.c
@@ -95,7 +95,15 @@ static inline u32 topo_apicid(u32 apicid, enum x86_topology_domains dom)
 	return apicid & (UINT_MAX << x86_topo_system.dom_shifts[dom - 1]);
 }
 
-static int topo_lookup_cpuid(u32 apic_id)
+/**
+ * topology_get_cpunr - Retrieve the CPU number for the given APIC ID
+ * @apic_id:		The APIC ID for which to lookup the CPU number
+ *
+ * Returns:
+ *  - >= 0:	The CPU number for the given APIC ID
+ *  - -ENODEV:	@apic_id does not match any known CPU
+ */
+int topology_get_cpunr(u32 apic_id)
 {
 	int i;
 
@@ -106,10 +114,11 @@ static int topo_lookup_cpuid(u32 apic_id)
 	}
 	return -ENODEV;
 }
+EXPORT_SYMBOL_GPL(topology_get_cpunr);
 
 static __init int topo_get_cpunr(u32 apic_id)
 {
-	int cpu = topo_lookup_cpuid(apic_id);
+	int cpu = topology_get_cpunr(apic_id);
 
 	if (cpu >= 0)
 		return cpu;
@@ -388,7 +397,7 @@ int topology_hotplug_apic(u32 apic_id, u32 acpi_id)
 	if (!test_bit(apic_id, apic_maps[TOPO_SMT_DOMAIN].map))
 		return -ENODEV;
 
-	cpu = topo_lookup_cpuid(apic_id);
+	cpu = topology_get_cpunr(apic_id);
 	if (cpu < 0)
 		return -ENOSPC;
 
-- 
2.34.1