arm: mxc: utilise usecount field in clock operations

This patch fixes the clock refcounting when reparenting is used.

Boot-tested on imx51 babbage board.

Sascha pointed out a good explanation of refcounting here:
http://www.spinics.net/lists/arm-kernel/msg85879.html

Signed-off-by: Amit Kucheria <amit.kucheria@canonical.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

1 files changed, 25 insertions, 12 deletions

diff --git a/arch/arm/plat-mxc/clock.c b/arch/arm/plat-mxc/clock.c
index 323ff8ccc877..2ed3ab173add 100644
--- a/arch/arm/plat-mxc/clock.c
+++ b/arch/arm/plat-mxc/clock.c
@@ -52,13 +52,14 @@ static void __clk_disable(struct clk *clk)
 {
         if (clk == NULL || IS_ERR(clk))
                 return;
-
-        __clk_disable(clk->parent);
-        __clk_disable(clk->secondary);
-
         WARN_ON(!clk->usecount);
-        if (!(--clk->usecount) && clk->disable)
-                clk->disable(clk);
+
+        if (!(--clk->usecount)) {
+                if (clk->disable)
+                        clk->disable(clk);
+                __clk_disable(clk->parent);
+                __clk_disable(clk->secondary);
+        }
 }
 
 static int __clk_enable(struct clk *clk)
@@ -66,12 +67,13 @@ static int __clk_enable(struct clk *clk)
         if (clk == NULL || IS_ERR(clk))
                 return -EINVAL;
 
-        __clk_enable(clk->parent);
-        __clk_enable(clk->secondary);
-
-        if (clk->usecount++ == 0 && clk->enable)
-                clk->enable(clk);
+        if (clk->usecount++ == 0) {
+                __clk_enable(clk->parent);
+                __clk_enable(clk->secondary);
 
+                if (clk->enable)
+                        clk->enable(clk);
+        }
         return 0;
 }
 
@@ -160,17 +162,28 @@ EXPORT_SYMBOL(clk_set_rate);
 int clk_set_parent(struct clk *clk, struct clk *parent)
 {
         int ret = -EINVAL;
+        struct clk *old;
 
         if (clk == NULL || IS_ERR(clk) || parent == NULL ||
             IS_ERR(parent) || clk->set_parent == NULL)
                 return ret;
 
+        if (clk->usecount)
+                clk_enable(parent);
+
         mutex_lock(&clocks_mutex);
         ret = clk->set_parent(clk, parent);
-        if (ret == 0)
+        if (ret == 0) {
+                old = clk->parent;
                 clk->parent = parent;
+        } else {
+                old = parent;
+        }
         mutex_unlock(&clocks_mutex);
 
+        if (clk->usecount)
+                clk_disable(old);
+
         return ret;
 }
 EXPORT_SYMBOL(clk_set_parent);