[PATCH v6 2/4] arch_topology: Support SMT control for OF based system

[Yicong Yang]

From: Yicong Yang <yangyicong@xxxxxxxxxxxxx>

On building the topology from the devicetree, we've already
gotten the SMT thread number of each core. Update the largest
SMT thread number and enable the SMT control by the end of
topology parsing.

The core's SMT control provides two interface to the users [1]:
1) enable/disable SMT by writing on/off
2) enable/disable SMT by writing thread number 1/max_thread_number

If a system have more than one SMT thread number the 2) may
not handle it well, since there're multiple thread numbers in the
system and 2) only accept 1/max_thread_number. So issue a warning
to notify the users if such system detected.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/ABI/testing/sysfs-devices-system-cpu#n542
Signed-off-by: Yicong Yang <yangyicong@xxxxxxxxxxxxx>
---
 drivers/base/arch_topology.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
index 75fcb75d5515..5eed864df5e6 100644
--- a/drivers/base/arch_topology.c
+++ b/drivers/base/arch_topology.c
@@ -11,6 +11,7 @@
 #include <linux/cleanup.h>
 #include <linux/cpu.h>
 #include <linux/cpufreq.h>
+#include <linux/cpu_smt.h>
 #include <linux/device.h>
 #include <linux/of.h>
 #include <linux/slab.h>
@@ -28,6 +29,7 @@
 static DEFINE_PER_CPU(struct scale_freq_data __rcu *, sft_data);
 static struct cpumask scale_freq_counters_mask;
 static bool scale_freq_invariant;
+static unsigned int max_smt_thread_num;
 DEFINE_PER_CPU(unsigned long, capacity_freq_ref) = 1;
 EXPORT_PER_CPU_SYMBOL_GPL(capacity_freq_ref);
 
@@ -561,6 +563,17 @@ static int __init parse_core(struct device_node *core, int package_id,
 		i++;
 	} while (1);
 
+	if (max_smt_thread_num < i)
+		max_smt_thread_num = i;
+
+	/*
+	 * If max_smt_thread_num has been initialized and doesn't match
+	 * the thread number of this entry, then the system has
+	 * heterogeneous SMT topology.
+	 */
+	if (max_smt_thread_num && max_smt_thread_num != i)
+		pr_warn_once("Heterogeneous SMT topology is partly supported by SMT control\n");
+
 	cpu = get_cpu_for_node(core);
 	if (cpu >= 0) {
 		if (!leaf) {
@@ -673,6 +686,14 @@ static int __init parse_socket(struct device_node *socket)
 	if (!has_socket)
 		ret = parse_cluster(socket, 0, -1, 0);
 
+	/*
+	 * Notify the CPU framework of the SMT support. A thread number of 1
+	 * can be handled by the framework so we don't need to check
+	 * max_smt_thread_num to see we support SMT or not.
+	 */
+	if (max_smt_thread_num)
+		cpu_smt_set_num_threads(max_smt_thread_num, max_smt_thread_num);
+
 	return ret;
 }
 
-- 
2.24.0