Patch "rtc-opal: Fix handling of firmware error codes, prevent busy loops" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

rtc-opal: Fix handling of firmware error codes, prevent busy loops

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
rtc-opal-fix-handling-of-firmware-error-codes-prevent-busy-loops.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Stewart Smith <[email protected]>
Date: Tue, 2 Aug 2016 11:50:16 +1000
Subject: rtc-opal: Fix handling of firmware error codes, prevent busy loops

From: Stewart Smith <[email protected]>

commit 5b8b58063029f02da573120ef4dc9079822e3cda upstream.

According to the OPAL docs:
skiboot-5.2.5/doc/opal-api/opal-rtc-read-3.txt
skiboot-5.2.5/doc/opal-api/opal-rtc-write-4.txt

OPAL_HARDWARE may be returned from OPAL_RTC_READ or OPAL_RTC_WRITE and this indicates either a transient or permanent error.

Prior to this patch, Linux was not dealing with OPAL_HARDWARE being a permanent error particularly well, in that you could end up in a busy loop.

This was not too hard to trigger on an AMI BMC based OpenPOWER machine doing a continuous "ipmitool mc reset cold" to the BMC, the result of that being that we'd get stuck in an infinite loop in opal_get_rtc_time().

We now retry a few times before returning the error higher up the stack.

---
 drivers/rtc/rtc-opal.c |   12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

@@ -58,6 +58,7 @@ static void tm_to_opal(struct rtc_time *
 static int opal_get_rtc_time(struct device *dev, struct rtc_time *tm)
 {
 	long rc = OPAL_BUSY;
+	int retries = 10;
 	u32 y_m_d;
 	u64 h_m_s_ms;
 	__be32 __y_m_d;

@@ -67,8 +68,11 @@ static int opal_get_rtc_time(struct devi
 		rc = opal_rtc_read(&__y_m_d, &__h_m_s_ms);
 		if (rc == OPAL_BUSY_EVENT)
 			opal_poll_events(NULL);
-		else
+		else if (retries-- && (rc == OPAL_HARDWARE
+				       || rc == OPAL_INTERNAL_ERROR))
 			msleep(10);
+		else if (rc != OPAL_BUSY && rc != OPAL_BUSY_EVENT)
+			break;
 	}
 
 	if (rc != OPAL_SUCCESS)

@@ -84,6 +88,7 @@ static int opal_get_rtc_time(struct devi
 static int opal_set_rtc_time(struct device *dev, struct rtc_time *tm)
 {
 	long rc = OPAL_BUSY;
+	int retries = 10;
 	u32 y_m_d = 0;
 	u64 h_m_s_ms = 0;
 

@@ -92,8 +97,11 @@ static int opal_set_rtc_time(struct devi
 		rc = opal_rtc_write(y_m_d, h_m_s_ms);
 		if (rc == OPAL_BUSY_EVENT)
 			opal_poll_events(NULL);
-		else
+		else if (retries-- && (rc == OPAL_HARDWARE
+				       || rc == OPAL_INTERNAL_ERROR))
 			msleep(10);
+		else if (rc != OPAL_BUSY && rc != OPAL_BUSY_EVENT)
+			break;
 	}
 
 	return rc == OPAL_SUCCESS ? 0 : -EIO;

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/rtc-opal-fix-handling-of-firmware-error-codes-prevent-busy-loops.patch