clk: Properly handle notifier return values

Notifiers may return NOTIFY_(OK|DONE|STOP|BAD). The CCF uses an
inconsistent mix of checking against NOTIFY_STOP or NOTIFY_BAD.
This inconsistency leaves errors undetected in some cases:
clk_set_parent() calls __clk_speculate_rates(), which stops when it
hits a NOTIFIER_BAD (STOP is ignored), and passes this value back to the
caller.
clk_set_parent() compares this return value against NOTIFY_STOP only,
ignoring NOTIFY_BAD returns.

Use NOTIFY_STOP_MASK to detect a negative notifier return value and
document all four return value options.

Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>

drivers/clk/clk.c

@@ -1027,16 +1027,16 @@ static int __clk_speculate_rates(struct clk *clk, unsigned long parent_rate)
 	else
 		new_rate = parent_rate;
 
-	/* abort the rate change if a driver returns NOTIFY_BAD */
+	/* abort rate change if a driver returns NOTIFY_BAD or NOTIFY_STOP */
 	if (clk->notifier_count)
 		ret = __clk_notify(clk, PRE_RATE_CHANGE, clk->rate, new_rate);
 
-	if (ret == NOTIFY_BAD)
+	if (ret & NOTIFY_STOP_MASK)
 		goto out;
 
 	hlist_for_each_entry(child, &clk->children, child_node) {
 		ret = __clk_speculate_rates(child, new_rate);
-		if (ret == NOTIFY_BAD)
+		if (ret & NOTIFY_STOP_MASK)
 			break;
 	}
 
@@ -1129,7 +1129,7 @@ static struct clk *clk_propagate_rate_change(struct clk *clk, unsigned long even
 
 	if (clk->notifier_count) {
 		ret = __clk_notify(clk, event, clk->rate, clk->new_rate);
-		if (ret == NOTIFY_BAD)
+		if (ret & NOTIFY_STOP_MASK)
 			fail_clk = clk;
 	}
 
@@ -1484,7 +1484,7 @@ int clk_set_parent(struct clk *clk, struct clk *parent)
 		ret = __clk_speculate_rates(clk, p_rate);
 
 	/* abort if a driver objects */
-	if (ret == NOTIFY_STOP)
+	if (ret & NOTIFY_STOP_MASK)
 		goto out;
 
 	/* do the re-parent */

include/linux/clk.h

@@ -28,16 +28,16 @@ struct clk;
  * PRE_RATE_CHANGE - called immediately before the clk rate is changed,
  *     to indicate that the rate change will proceed.  Drivers must
  *     immediately terminate any operations that will be affected by the
- *     rate change.  Callbacks may either return NOTIFY_DONE or
- *     NOTIFY_STOP.
+ *     rate change.  Callbacks may either return NOTIFY_DONE, NOTIFY_OK,
+ *     NOTIFY_STOP or NOTIFY_BAD.
  *
  * ABORT_RATE_CHANGE: called if the rate change failed for some reason
  *     after PRE_RATE_CHANGE.  In this case, all registered notifiers on
  *     the clk will be called with ABORT_RATE_CHANGE. Callbacks must
- *     always return NOTIFY_DONE.
+ *     always return NOTIFY_DONE or NOTIFY_OK.
  *
  * POST_RATE_CHANGE - called after the clk rate change has successfully
- *     completed.  Callbacks must always return NOTIFY_DONE.
+ *     completed.  Callbacks must always return NOTIFY_DONE or NOTIFY_OK.
  *
  */
 #define PRE_RATE_CHANGE			BIT(0)