[PATCH v7 1/9] x86/topology: Export topo_lookup_cpuid() for resctrl use

[Chen Yu <yu.c.chen@intel.com>]

Enhanced RDT (ERDT) enumerates its monitoring and control resources through
ACPI tables that identify each CPU by its x2APIC ID. To associate this
firmware-provided data with the kernel's per-CPU structures, ERDT must
translate those x2APIC IDs into logical CPU numbers.

topo_lookup_cpuid() already performs this translation, but it is static to
topology.c and therefore not reachable from resctrl.

Export topo_lookup_cpuid() and add its declaration to asm/apic.h that already
exposes the inverse mapping via cpuid_to_apicid[], so that ERDT can resolve
x2APIC IDs from ACPI tables to logical CPU numbers.

No functional change intended.

Signed-off-by: Chen Yu <yu.c.chen@intel.com>
Tested-by: Hongyu Ning <hongyu.ning@linux.intel.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
---
v6->v7:
    Add motivation for choosing asm/apic.h, which already exposes the
    inverse mapping via cpuid_to_apicid[]. (Reinette Chatre)
---
 arch/x86/include/asm/apic.h    | 1 +
 arch/x86/kernel/cpu/topology.c | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
index 9cd493d467d4..bb84651b14bd 100644
--- a/arch/x86/include/asm/apic.h
+++ b/arch/x86/include/asm/apic.h
@@ -54,6 +54,7 @@ static inline void x86_32_probe_apic(void) { }
 #endif
 
 extern u32 cpuid_to_apicid[];
+int topo_lookup_cpuid(u32 apic_id);
 
 #define CPU_ACPIID_INVALID	U32_MAX
 
diff --git a/arch/x86/kernel/cpu/topology.c b/arch/x86/kernel/cpu/topology.c
index 4913b64ec592..bcee70fb9277 100644
--- a/arch/x86/kernel/cpu/topology.c
+++ b/arch/x86/kernel/cpu/topology.c
@@ -92,7 +92,7 @@ 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)
+int topo_lookup_cpuid(u32 apic_id)
 {
 	int i;
 
-- 
2.25.1