opal: Fix hang in time_wait* calls on HMI for TB errors.

On TOD/TB errors timebase register stops/freezes until HMI error recovery
gets TOD/TB back into running state. However, while HMI recovery is in
progress there are chances where some code path may invoke time_wait*()
calls which depends on running TB value. In an event of TB not moving,
time_wait* calls would keep looping resulting into a hang on that CPU.

On OpenPower systems we are seeing system hang on TOD/TB errors. The hang
is seen inside OPAL HMI handler while invoking prlog/perror(). The reason
is, on OpenPower systems prlog/perror() depends on LPC UART console
driver to flush log messages to the console. UART read/write calls invoke
time_wait_nopoll() inside opb_[read|write]() functions. When TB is in
stopped state this causes a hang in prlog/perror() calls.

This patch fixes this issue by modifying time_wait_[no]poll() to check
for TB validity and return immediately.

Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/core/timebase.c b/core/timebase.c
index b1d8196..4fcfae5 100644
--- a/core/timebase.c
+++ b/core/timebase.c
@@ -25,6 +25,11 @@ static void time_wait_poll(unsigned long duration)
 	unsigned long end = mftb() + duration;
 	unsigned long period = msecs_to_tb(5);
 
+	if (this_cpu()->tb_invalid) {
+		cpu_relax();
+		return;
+	}
+
 	while (tb_compare(mftb(), end) != TB_AAFTERB) {
 		/* Call pollers periodically but not continually to avoid
 		 * bouncing cachelines due to lock contention. */
@@ -57,6 +62,11 @@ void time_wait_nopoll(unsigned long duration)
 {
 	unsigned long end = mftb() + duration;
 
+	if (this_cpu()->tb_invalid) {
+		cpu_relax();
+		return;
+	}
+
 	while(tb_compare(mftb(), end) != TB_AAFTERB)
 		cpu_relax();
 }