rtc: opal: Fix OPAL RTC driver OPAL_BUSY loops

The OPAL RTC driver does not sleep in case it gets OPAL_BUSY or
OPAL_BUSY_EVENT from firmware, which causes large scheduling
latencies, up to 50 seconds have been observed here when RTC stops
responding (BMC reboot can do it).

Fix this by converting it to the standard form OPAL_BUSY loop that
sleeps.

Fixes: 628daa8d5abf ("powerpc/powernv: Add RTC and NVRAM support plus RTAS fallbacks")
Cc: stable@vger.kernel.org # v3.2+
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/powernv/opal-rtc.c

@@ -48,10 +48,12 @@ unsigned long __init opal_get_boot_time(void)
 
 	while (rc == OPAL_BUSY || rc == OPAL_BUSY_EVENT) {
 		rc = opal_rtc_read(&__y_m_d, &__h_m_s_ms);
-		if (rc == OPAL_BUSY_EVENT)
+		if (rc == OPAL_BUSY_EVENT) {
+			mdelay(OPAL_BUSY_DELAY_MS);
 			opal_poll_events(NULL);
-		else if (rc == OPAL_BUSY)
-			mdelay(10);
+		} else if (rc == OPAL_BUSY) {
+			mdelay(OPAL_BUSY_DELAY_MS);
+		}
 	}
 	if (rc != OPAL_SUCCESS)
 		return 0;

drivers/rtc/rtc-opal.c

@@ -57,7 +57,7 @@ static void tm_to_opal(struct rtc_time *tm, u32 *y_m_d, u64 *h_m_s_ms)
 
 static int opal_get_rtc_time(struct device *dev, struct rtc_time *tm)
 {
-	long rc = OPAL_BUSY;
+	s64 rc = OPAL_BUSY;
 	int retries = 10;
 	u32 y_m_d;
 	u64 h_m_s_ms;
@@ -66,13 +66,17 @@ static int opal_get_rtc_time(struct device *dev, struct rtc_time *tm)
 
 	while (rc == OPAL_BUSY || rc == OPAL_BUSY_EVENT) {
 		rc = opal_rtc_read(&__y_m_d, &__h_m_s_ms);
-		if (rc == OPAL_BUSY_EVENT)
+		if (rc == OPAL_BUSY_EVENT) {
+			msleep(OPAL_BUSY_DELAY_MS);
 			opal_poll_events(NULL);
-		else if (retries-- && (rc == OPAL_HARDWARE
-				       || rc == OPAL_INTERNAL_ERROR))
-			msleep(10);
-		else if (rc != OPAL_BUSY && rc != OPAL_BUSY_EVENT)
-			break;
+		} else if (rc == OPAL_BUSY) {
+			msleep(OPAL_BUSY_DELAY_MS);
+		} else if (rc == OPAL_HARDWARE || rc == OPAL_INTERNAL_ERROR) {
+			if (retries--) {
+				msleep(10); /* Wait 10ms before retry */
+				rc = OPAL_BUSY; /* go around again */
+			}
+		}
 	}
 
 	if (rc != OPAL_SUCCESS)
@@ -87,21 +91,26 @@ static int opal_get_rtc_time(struct device *dev, struct rtc_time *tm)
 
 static int opal_set_rtc_time(struct device *dev, struct rtc_time *tm)
 {
-	long rc = OPAL_BUSY;
+	s64 rc = OPAL_BUSY;
 	int retries = 10;
 	u32 y_m_d = 0;
 	u64 h_m_s_ms = 0;
 
 	tm_to_opal(tm, &y_m_d, &h_m_s_ms);
+
 	while (rc == OPAL_BUSY || rc == OPAL_BUSY_EVENT) {
 		rc = opal_rtc_write(y_m_d, h_m_s_ms);
-		if (rc == OPAL_BUSY_EVENT)
+		if (rc == OPAL_BUSY_EVENT) {
+			msleep(OPAL_BUSY_DELAY_MS);
 			opal_poll_events(NULL);
-		else if (retries-- && (rc == OPAL_HARDWARE
-				       || rc == OPAL_INTERNAL_ERROR))
-			msleep(10);
-		else if (rc != OPAL_BUSY && rc != OPAL_BUSY_EVENT)
-			break;
+		} else if (rc == OPAL_BUSY) {
+			msleep(OPAL_BUSY_DELAY_MS);
+		} else if (rc == OPAL_HARDWARE || rc == OPAL_INTERNAL_ERROR) {
+			if (retries--) {
+				msleep(10); /* Wait 10ms before retry */
+				rc = OPAL_BUSY; /* go around again */
+			}
+		}
 	}
 
 	return rc == OPAL_SUCCESS ? 0 : -EIO;