[RFC PATCH 06/10] ARM: sched: Use device-tree to provide fast/slow CPU list for HMP

[morten.rasmussen@arm.com]

From: Morten Rasmussen <morten.rasmussen@arm.com>

We can't rely on Kconfig options to set the fast and slow CPU lists for
HMP scheduling if we want a single kernel binary to support multiple
devices with different CPU topology. E.g. TC2 (ARM's Test-Chip-2
big.LITTLE system), Fast Models, or even non big.LITTLE devices.

This patch adds the function arch_get_fast_and_slow_cpus() to generate
the lists at run-time by parsing the CPU nodes in device-tree; it
assumes slow cores are A7s and everything else is fast. The function
still supports the old Kconfig options as this is useful for testing the
HMP scheduler on devices without big.LITTLE.

This patch is reuse of a patch by Jon Medhurst <tixy@linaro.org> with a
few bits left out.

Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
---
 arch/arm/Kconfig           |    4 ++-
 arch/arm/kernel/topology.c |   69 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 72 insertions(+), 1 deletion(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index cb80846..f1271bc 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1588,13 +1588,15 @@ config HMP_FAST_CPU_MASK
 	string "HMP scheduler fast CPU mask"
 	depends on SCHED_HMP
 	help
-          Specify the cpuids of the fast CPUs in the system as a list string,
+          Leave empty to use device tree information.
+	  Specify the cpuids of the fast CPUs in the system as a list string,
 	  e.g. cpuid 0+1 should be specified as 0-1.
 
 config HMP_SLOW_CPU_MASK
 	string "HMP scheduler slow CPU mask"
 	depends on SCHED_HMP
 	help
+	  Leave empty to use device tree information.
 	  Specify the cpuids of the slow CPUs in the system as a list string,
 	  e.g. cpuid 0+1 should be specified as 0-1.
 
diff --git a/arch/arm/kernel/topology.c b/arch/arm/kernel/topology.c
index 26c12c6..7682e12 100644
--- a/arch/arm/kernel/topology.c
+++ b/arch/arm/kernel/topology.c
@@ -317,6 +317,75 @@ void store_cpu_topology(unsigned int cpuid)
 		cpu_topology[cpuid].socket_id, mpidr);
 }
 
+
+#ifdef CONFIG_SCHED_HMP
+
+static const char * const little_cores[] = {
+	"arm,cortex-a7",
+	NULL,
+};
+
+static bool is_little_cpu(struct device_node *cn)
+{
+	const char * const *lc;
+	for (lc = little_cores; *lc; lc++)
+		if (of_device_is_compatible(cn, *lc))
+			return true;
+	return false;
+}
+
+void __init arch_get_fast_and_slow_cpus(struct cpumask *fast,
+					struct cpumask *slow)
+{
+	struct device_node *cn = NULL;
+	int cpu = 0;
+
+	cpumask_clear(fast);
+	cpumask_clear(slow);
+
+	/*
+	 * Use the config options if they are given. This helps testing
+	 * HMP scheduling on systems without a big.LITTLE architecture.
+	 */
+	if (strlen(CONFIG_HMP_FAST_CPU_MASK) && strlen(CONFIG_HMP_SLOW_CPU_MASK)) {
+		if (cpulist_parse(CONFIG_HMP_FAST_CPU_MASK, fast))
+			WARN(1, "Failed to parse HMP fast cpu mask!\n");
+		if (cpulist_parse(CONFIG_HMP_SLOW_CPU_MASK, slow))
+			WARN(1, "Failed to parse HMP slow cpu mask!\n");
+		return;
+	}
+
+	/*
+	 * Else, parse device tree for little cores.
+	 */
+	while ((cn = of_find_node_by_type(cn, "cpu"))) {
+
+		if (cpu >= num_possible_cpus())
+			break;
+
+		if (is_little_cpu(cn))
+			cpumask_set_cpu(cpu, slow);
+		else
+			cpumask_set_cpu(cpu, fast);
+
+		cpu++;
+	}
+
+	if (!cpumask_empty(fast) && !cpumask_empty(slow))
+		return;
+
+	/*
+	 * We didn't find both big and little cores so let's call all cores
+	 * fast as this will keep the system running, with all cores being
+	 * treated equal.
+	 */
+	cpumask_setall(fast);
+	cpumask_clear(slow);
+}
+
+#endif /* CONFIG_SCHED_HMP */
+
+
 /*
  * init_cpu_topology is called at boot when only one cpu is running
  * which prevent simultaneous write access to cpu_topology array
-- 
1.7.9.5