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From:   Conor Dooley <mail@conchuod.ie>
To:     Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Palmer Dabbelt <palmer@rivosinc.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Sudeep Holla <sudeep.holla@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J . Wysocki" <rafael@kernel.org>
Cc:     Daire McNamara <daire.mcnamara@microchip.com>,
        Conor Dooley <conor.dooley@microchip.com>,
        Niklas Cassel <niklas.cassel@wdc.com>,
        Damien Le Moal <damien.lemoal@opensource.wdc.com>,
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        linux-arm-kernel@lists.infradead.org,
        Brice Goglin <Brice.Goglin@inria.fr>
Subject: [PATCH v2 1/2] arm64: topology: move store_cpu_topology() to shared code
Date:   Fri,  8 Jul 2022 21:33:42 +0100
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From: Conor Dooley <conor.dooley@microchip.com>

arm64's method of defining a default cpu topology requires only minimal
changes to apply to RISC-V also. The current arm64 implementation exits
early in a uniprocessor configuration by reading MPIDR & claiming that
uniprocessor can rely on the default values.

This is appears to be a hangover from prior to '3102bc0e6ac7 ("arm64:
topology: Stop using MPIDR for topology information")', because the
current code just assigns default values for multiprocessor systems.

With the MPIDR references removed, store_cpu_topolgy() can be moved to
the common arch_topology code.

CC: stable@vger.kernel.org
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
---
 arch/arm64/kernel/topology.c | 40 ------------------------------------
 drivers/base/arch_topology.c | 19 +++++++++++++++++
 2 files changed, 19 insertions(+), 40 deletions(-)

diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index 869ffc4d4484..7889a00f5487 100644
--- a/arch/arm64/kernel/topology.c
+++ b/arch/arm64/kernel/topology.c
@@ -22,46 +22,6 @@
 #include <asm/cputype.h>
 #include <asm/topology.h>
 
-void store_cpu_topology(unsigned int cpuid)
-{
-	struct cpu_topology *cpuid_topo = &cpu_topology[cpuid];
-	u64 mpidr;
-
-	if (cpuid_topo->package_id != -1)
-		goto topology_populated;
-
-	mpidr = read_cpuid_mpidr();
-
-	/* Uniprocessor systems can rely on default topology values */
-	if (mpidr & MPIDR_UP_BITMASK)
-		return;
-
-	/*
-	 * This would be the place to create cpu topology based on MPIDR.
-	 *
-	 * However, it cannot be trusted to depict the actual topology; some
-	 * pieces of the architecture enforce an artificial cap on Aff0 values
-	 * (e.g. GICv3's ICC_SGI1R_EL1 limits it to 15), leading to an
-	 * artificial cycling of Aff1, Aff2 and Aff3 values. IOW, these end up
-	 * having absolutely no relationship to the actual underlying system
-	 * topology, and cannot be reasonably used as core / package ID.
-	 *
-	 * If the MT bit is set, Aff0 *could* be used to define a thread ID, but
-	 * we still wouldn't be able to obtain a sane core ID. This means we
-	 * need to entirely ignore MPIDR for any topology deduction.
-	 */
-	cpuid_topo->thread_id  = -1;
-	cpuid_topo->core_id    = cpuid;
-	cpuid_topo->package_id = cpu_to_node(cpuid);
-
-	pr_debug("CPU%u: cluster %d core %d thread %d mpidr %#016llx\n",
-		 cpuid, cpuid_topo->package_id, cpuid_topo->core_id,
-		 cpuid_topo->thread_id, mpidr);
-
-topology_populated:
-	update_siblings_masks(cpuid);
-}
-
 #ifdef CONFIG_ACPI
 static bool __init acpi_cpu_is_threaded(int cpu)
 {
diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
index 441e14ac33a4..07e84c6ac5c2 100644
--- a/drivers/base/arch_topology.c
+++ b/drivers/base/arch_topology.c
@@ -765,6 +765,25 @@ void update_siblings_masks(unsigned int cpuid)
 	}
 }
 
+void __weak 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);
+}
+
 static void clear_cpu_topology(int cpu)
 {
 	struct cpu_topology *cpu_topo = &cpu_topology[cpu];
-- 
2.37.0