1 files changed, 32 insertions, 2 deletions

diff --git a/drivers/clocksource/sh_cmt.c b/drivers/clocksource/sh_cmt.c
index dc7c033ef587..32a77becc098 100644
--- a/drivers/clocksource/sh_cmt.c
+++ b/drivers/clocksource/sh_cmt.c
@@ -26,6 +26,7 @@
 #include <linux/clk.h>
 #include <linux/irq.h>
 #include <linux/err.h>
+#include <linux/delay.h>
 #include <linux/clocksource.h>
 #include <linux/clockchips.h>
 #include <linux/sh_timer.h>
@@ -150,13 +151,13 @@ static void sh_cmt_start_stop_ch(struct sh_cmt_priv *p, int start)
 
 static int sh_cmt_enable(struct sh_cmt_priv *p, unsigned long *rate)
 {
-        int ret;
+        int k, ret;
 
         /* enable clock */
         ret = clk_enable(p->clk);
         if (ret) {
                 dev_err(&p->pdev->dev, "cannot enable clock\n");
-                return ret;
+                goto err0;
         }
 
         /* make sure channel is disabled */
@@ -174,9 +175,38 @@ static int sh_cmt_enable(struct sh_cmt_priv *p, unsigned long *rate)
         sh_cmt_write(p, CMCOR, 0xffffffff);
         sh_cmt_write(p, CMCNT, 0);
 
+        /*
+         * According to the sh73a0 user's manual, as CMCNT can be operated
+         * only by the RCLK (Pseudo 32 KHz), there's one restriction on
+         * modifying CMCNT register; two RCLK cycles are necessary before
+         * this register is either read or any modification of the value
+         * it holds is reflected in the LSI's actual operation.
+         *
+         * While at it, we're supposed to clear out the CMCNT as of this
+         * moment, so make sure it's processed properly here.  This will
+         * take RCLKx2 at maximum.
+         */
+        for (k = 0; k < 100; k++) {
+                if (!sh_cmt_read(p, CMCNT))
+                        break;
+                udelay(1);
+        }
+
+        if (sh_cmt_read(p, CMCNT)) {
+                dev_err(&p->pdev->dev, "cannot clear CMCNT\n");
+                ret = -ETIMEDOUT;
+                goto err1;
+        }
+
         /* enable channel */
         sh_cmt_start_stop_ch(p, 1);
         return 0;
+ err1:
+        /* stop clock */
+        clk_disable(p->clk);
+
+ err0:
+        return ret;
 }
 
 static void sh_cmt_disable(struct sh_cmt_priv *p)