smptest: Add a check for active cpus.

build-config-kerneltests currently specifies that this test needs 4 CPUs
and should only be run on systems that have at least 4 CPUs. The test
used to fail if fewer CPUs were online, but when the test was modified
to test all active CPUs it lost the ability to detect that CPUs that are
meant to be active never activated. Add a new build flag to specify how
many CPUs are expected to be online, with a default value of 4 to match
build-config-kerneltests, and a test to check that at least this many
CPUs are active.

Bug: None
Change-Id: I2d1e17339d83126c49fd948635aaba6d216b1889

app/smptest/rules.mk

diff --git a/app/smptest/rules.mk b/app/smptest/rules.mk
index 166630b..36aadac 100644
--- a/app/smptest/rules.mk
+++ b/app/smptest/rules.mk
@@ -10,6 +10,11 @@
 MODULE_SRCS += \
 	$(LOCAL_DIR)/smptest.c \
 
+SMPTEST_MIN_CPU_COUNT ?= 4
+
+MODULE_DEFINES += \
+	SMPTEST_MIN_CPU_COUNT=$(SMPTEST_MIN_CPU_COUNT) \
+
 include make/module.mk
 
 endif

app/smptest/smptest.c

diff --git a/app/smptest/smptest.c b/app/smptest/smptest.c
index 6551df9..9b44f07 100644
--- a/app/smptest/smptest.c
+++ b/app/smptest/smptest.c
@@ -114,6 +114,16 @@
     return 0;
 }
 
+TEST(smptest, check_cpu_active) {
+    uint active_cpu_count = 0;
+    for (uint i = 0; i < SMP_MAX_CPUS; i++) {
+        if (mp_is_cpu_active(i)) {
+            active_cpu_count++;
+        }
+    }
+    EXPECT_GE(active_cpu_count, SMPTEST_MIN_CPU_COUNT);
+}
+
 TEST(smptest, run) {
     bool wait_for_cpus = false;