cpufreq_dt: Do not attach the device if the cpu isn't present

If we boot with hw.ncpu=X (available on arm and arm64 at least) we
shouldn't attach the cpufreq driver as cf_set_method will try to get
the cpuid and it doesn't exists.
This solves cpufreq panicing on RockChip RK3399 when booting with
hw.ncpu=4

MFC after:	1 week

1 files changed, 9 insertions, 2 deletions

diff --git a/sys/dev/cpufreq/cpufreq_dt.c b/sys/dev/cpufreq/cpufreq_dt.c
index 0633184fe618..061345f1bfca 100644
--- a/sys/dev/cpufreq/cpufreq_dt.c
+++ b/sys/dev/cpufreq/cpufreq_dt.c
@@ -446,7 +446,7 @@ cpufreq_dt_attach(device_t dev)
 	struct cpufreq_dt_softc *sc;
 	phandle_t node;
 	phandle_t cnode, opp, copp;
-	int cpu;
+	int cpu, ncpu;
 	uint64_t freq;
 	int rv = 0;
 	enum opp_version version;
@@ -454,6 +454,14 @@ cpufreq_dt_attach(device_t dev)
 	sc = device_get_softc(dev);
 	sc->dev = dev;
 	node = ofw_bus_get_node(device_get_parent(dev));
+	cpu = device_get_unit(device_get_parent(dev));
+
+	if (TUNABLE_INT_FETCH("hw.ncpu", &ncpu)) {
+		if (cpu >= ncpu) {
+			device_printf(dev, "Not attaching as cpu is not present\n");
+			return (ENXIO);
+		}
+	}
 
 	if (regulator_get_by_ofw_property(dev, node,
 	    "cpu-supply", &sc->reg) != 0) {
@@ -496,7 +504,6 @@ cpufreq_dt_attach(device_t dev)
 	 * Find all CPUs that share the same opp table
 	 */
 	CPU_ZERO(&sc->cpus);
-	cpu = device_get_unit(device_get_parent(dev));
 	for (cnode = node; cnode > 0; cnode = OF_peer(cnode), cpu++) {
 		copp = -1;
 		if (version == OPP_V1)