[Arm-dev] [PATCH v1 58/87] clocksource: arm_arch_timer: fix system hang

[Vadim Lomovtsev]

From: Al Stone <ahs3 at redhat.com>

Arm allows for two possible architectural clock sources. One memory mapped
and the other coprocessor based. If both timers exist, then the driver waits
for both to be probed before registering a clocksource.

Commit c387f07e6205 ("clocksource: arm_arch_timer: Discard unavailable timers
correctly") attempted to fix a hang occurring when one of the two possible
timers had a device node, but was disabled. In that case, the second probe
would never occur and the system would hang without a clocksource being
registered.

Unfortunately, incorrect logic in that commit made things worse such that
a hang would occur unless both timers had a device node and were enabled.
This patch fixes the logic so that we don't wait to probe a second timer
unless it exists and is enabled.

Signed-off-by: Mark Salter <msalter at redhat.com>
Signed-off-by: Vadim Lomovtsev <Vadim.Lomovtsev at caviumnetworks.com>
---
 drivers/clocksource/arm_arch_timer.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index 0aa135d..17ad6f4 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -672,10 +672,11 @@ arch_timer_needs_probing(int type, const struct of_device_id *matches)
 	bool needs_probing = false;
 
 	dn = of_find_matching_node(NULL, matches);
-	if (dn && of_device_is_available(dn) && !(arch_timers_present & type))
-		needs_probing = true;
-	of_node_put(dn);
-
+	if (dn) {
+		if (dn && of_device_is_available(dn) && !(arch_timers_present & type))
+			needs_probing = true;
+		of_node_put(dn);
+	}
 	return needs_probing;
 }
 
-- 
2.4.3