drivers/rtc/rtc-pl031.c: fix the missing operation on enable

The RTC control register should be enabled in the process of
initializing.

Without this patch, I failed to enable RTC in Hisilicon Hi3620 SoC.  The
register mapping section in RTC is always read as zero.  So I doubt that
ST guys may already enable this register in bootloader.  So they won't
meet this issue.

Signed-off-by: Haojian Zhuang <haojian.zhuang@linaro.org>
Cc: Srinidhi Kasagar <srinidhi.kasagar@stericsson.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 3 deletions

diff --git a/drivers/rtc/rtc-pl031.c b/drivers/rtc/rtc-pl031.c
index 08378e3cc21c..10c1a3454e48 100644
--- a/drivers/rtc/rtc-pl031.c
+++ b/drivers/rtc/rtc-pl031.c
@@ -44,6 +44,7 @@
 #define RTC_YMR         0x34    /* Year match register */
 #define RTC_YLR         0x38    /* Year data load register */
 
+#define RTC_CR_EN       (1 << 0)        /* counter enable bit */
 #define RTC_CR_CWEN     (1 << 26)       /* Clockwatch enable bit */
 
 #define RTC_TCR_EN      (1 << 1) /* Periodic timer enable bit */
@@ -320,7 +321,7 @@ static int pl031_probe(struct amba_device *adev, const struct amba_id *id)
         struct pl031_local *ldata;
         struct pl031_vendor_data *vendor = id->data;
         struct rtc_class_ops *ops = &vendor->ops;
-        unsigned long time;
+        unsigned long time, data;
 
         ret = amba_request_regions(adev, NULL);
         if (ret)
@@ -345,10 +346,11 @@ static int pl031_probe(struct amba_device *adev, const struct amba_id *id)
         dev_dbg(&adev->dev, "designer ID = 0x%02x\n", amba_manf(adev));
         dev_dbg(&adev->dev, "revision = 0x%01x\n", amba_rev(adev));
 
+        data = readl(ldata->base + RTC_CR);
         /* Enable the clockwatch on ST Variants */
         if (vendor->clockwatch)
-                writel(readl(ldata->base + RTC_CR) | RTC_CR_CWEN,
-                       ldata->base + RTC_CR);
+                data |= RTC_CR_CWEN;
+        writel(data | RTC_CR_EN, ldata->base + RTC_CR);
 
         /*
          * On ST PL031 variants, the RTC reset value does not provide correct