linux-kernel - [PATCH] arm64: of: handle multiple threads in ARM cpu node

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Message-ID: <20250110161057.445-1-alireza.sanaee@huawei.com>
Date: Fri, 10 Jan 2025 16:10:57 +0000
From: Alireza Sanaee <alireza.sanaee@...wei.com>
To: <devicetree@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>
CC: <robh@...nel.org>, <linuxarm@...wei.com>,
	<shameerali.kolothum.thodi@...wei.com>, <Jonathan.Cameron@...wei.com>,
	<jiangkunkun@...wei.com>, <yangyicong@...ilicon.com>
Subject: [PATCH] arm64: of: handle multiple threads in ARM cpu node

Update `of_parse_and_init_cpus` to parse reg property of CPU node as
an array based as per spec for SMT threads.

Spec v0.4 Section 3.8.1:
The value of reg is a <prop-encoded-**array**> that defines a unique
CPU/thread id for the CPU/threads represented by the CPU node.  **If a CPU
supports more than one thread (i.e.  multiple streams of execution) the
reg property is an array with 1 element per thread**.  The address-cells
on the /cpus node specifies how many cells each element of the array
takes. Software can determine the number of threads by dividing the size
of reg by the parent node's address-cells.

An accurate example of 1 core with 2 SMTs:

	cpus {
		#size-cells = <0x00>;
		#address-cells = <0x01>;

		cpu@0 {
			phandle = <0x8000>;
			**reg = <0x00 0x01>;**
			enable-method = "psci";
			compatible = "arm,cortex-a57";
			device_type = "cpu";
		};
	};

Instead of:

	cpus {
		#size-cells = <0x00>;
		#address-cells = <0x01>;

		cpu@0 {
			phandle = <0x8000>;
			reg = <0x00>;
			enable-method = "psci";
			compatible = "arm,cortex-a57";
			device_type = "cpu";
		};

		cpu@1 {
			phandle = <0x8001>;
			reg = <0x01>;
			enable-method = "psci";
			compatible = "arm,cortex-a57";
			device_type = "cpu";
		};
	};

which is **NOT** accurate.

Signed-off-by: Alireza Sanaee <alireza.sanaee@...wei.com>
---
 arch/arm64/kernel/smp.c | 74 +++++++++++++++++++++++------------------
 1 file changed, 41 insertions(+), 33 deletions(-)

diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 3b3f6b56e733..8dd3b3c82967 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -689,53 +689,61 @@ static void __init acpi_parse_and_init_cpus(void)
 static void __init of_parse_and_init_cpus(void)
 {
 	struct device_node *dn;
+	u64 hwid;
+	u32 tid;
 
 	for_each_of_cpu_node(dn) {
-		u64 hwid = of_get_cpu_hwid(dn, 0);
+		tid = 0;
 
-		if (hwid & ~MPIDR_HWID_BITMASK)
-			goto next;
+		while (1) {
+			hwid = of_get_cpu_hwid(dn, tid++);
+			if (hwid == ~0ULL)
+				break;
 
-		if (is_mpidr_duplicate(cpu_count, hwid)) {
-			pr_err("%pOF: duplicate cpu reg properties in the DT\n",
-				dn);
-			goto next;
-		}
+			if (hwid & ~MPIDR_HWID_BITMASK)
+				goto next;
 
-		/*
-		 * The numbering scheme requires that the boot CPU
-		 * must be assigned logical id 0. Record it so that
-		 * the logical map built from DT is validated and can
-		 * be used.
-		 */
-		if (hwid == cpu_logical_map(0)) {
-			if (bootcpu_valid) {
-				pr_err("%pOF: duplicate boot cpu reg property in DT\n",
-					dn);
+			if (is_mpidr_duplicate(cpu_count, hwid)) {
+				pr_err("%pOF: duplicate cpu reg properties in the DT\n",
+				       dn);
 				goto next;
 			}
 
-			bootcpu_valid = true;
-			early_map_cpu_to_node(0, of_node_to_nid(dn));
-
 			/*
-			 * cpu_logical_map has already been
-			 * initialized and the boot cpu doesn't need
-			 * the enable-method so continue without
-			 * incrementing cpu.
+			 * The numbering scheme requires that the boot CPU
+			 * must be assigned logical id 0. Record it so that
+			 * the logical map built from DT is validated and can
+			 * be used.
 			 */
-			continue;
-		}
+			if (hwid == cpu_logical_map(0)) {
+				if (bootcpu_valid) {
+					pr_err("%pOF: duplicate boot cpu reg property in DT\n",
+					       dn);
+					goto next;
+				}
+
+				bootcpu_valid = true;
+				early_map_cpu_to_node(0, of_node_to_nid(dn));
+
+				/*
+				 * cpu_logical_map has already been
+				 * initialized and the boot cpu doesn't need
+				 * the enable-method so continue without
+				 * incrementing cpu.
+				 */
+				continue;
+			}
 
-		if (cpu_count >= NR_CPUS)
-			goto next;
+			if (cpu_count >= NR_CPUS)
+				goto next;
 
-		pr_debug("cpu logical map 0x%llx\n", hwid);
-		set_cpu_logical_map(cpu_count, hwid);
+			pr_debug("cpu logical map 0x%llx\n", hwid);
+			set_cpu_logical_map(cpu_count, hwid);
 
-		early_map_cpu_to_node(cpu_count, of_node_to_nid(dn));
+			early_map_cpu_to_node(cpu_count, of_node_to_nid(dn));
 next:
-		cpu_count++;
+			cpu_count++;
+		}
 	}
 }
 
-- 
2.43.0