[PATCH 3/7] rtc: davinci: check BUSY bit before set TC registers

[Dario Binacchi]

To write correct data to the TC registers, the STATUS register must be
read until the BUSY bit is equal to zero. Once the BUSY flag is zero,
there is a 15 μs access period in which the TC registers can be
programmed.
The rtc_wait_not_busy() has been inspired by the Kernel.

Signed-off-by: Dario Binacchi <dario...@libero.it>
---

 drivers/rtc/davinci.c | 45 ++++++++++++++++++++++++++++++++++---------
 1 file changed, 36 insertions(+), 9 deletions(-)

diff --git a/drivers/rtc/davinci.c b/drivers/rtc/davinci.c
index 99ae31e2a5..7b8c729f3b 100644
--- a/drivers/rtc/davinci.c
+++ b/drivers/rtc/davinci.c
@@ -16,19 +16,39 @@
 #define RTC_BASE DAVINCI_RTC_BASE
 #endif
 
-int rtc_get(struct rtc_time *tmp)
+static int davinci_rtc_wait_not_busy(struct davinci_rtc *rtc)
 {
-       struct davinci_rtc *rtc = (struct davinci_rtc *)RTC_BASE;
-       unsigned long sec, min, hour, mday, wday, mon_cent, year;
-       unsigned long status;
+       int count;
+       u8 status;
 
        status = readb(&rtc->status);
        if ((status & RTC_STATE_RUN) != RTC_STATE_RUN) {
                printf("RTC doesn't run\n");
                return -1;
        }
-       if ((status & RTC_STATE_BUSY) == RTC_STATE_BUSY)
-               udelay(20);
+
+       /* BUSY may stay active for 1/32768 second (~30 usec) */
+       for (count = 0; count < 50; count++) {
+               if (!(status & RTC_STATE_BUSY))
+                       break;
+
+               udelay(1);
+               status = readb(&rtc->status);
+       }
+
+       /* now we have ~15 usec to read/write various registers */
+       return 0;
+}
+
+int rtc_get(struct rtc_time *tmp)
+{
+       struct davinci_rtc *rtc = (struct davinci_rtc *)RTC_BASE;
+       unsigned long sec, min, hour, mday, wday, mon_cent, year;
+       int ret;
+
+       ret = davinci_rtc_wait_not_busy(rtc);
+       if (ret)
+               return ret;
 
        sec     = readb(&rtc->second);
        min     = readb(&rtc->minutes);
@@ -63,10 +83,12 @@ int rtc_get(struct rtc_time *tmp)
 int rtc_set(struct rtc_time *tmp)
 {
        struct davinci_rtc *rtc = (struct davinci_rtc *)RTC_BASE;
+       int ret;
+
+       ret = davinci_rtc_wait_not_busy(rtc);
+       if (ret)
+               return ret;
 
-       debug("Set DATE: %4d-%02d-%02d (wday=%d)  TIME: %2d:%02d:%02d\n",
-               tmp->tm_year, tmp->tm_mon, tmp->tm_mday, tmp->tm_wday,
-               tmp->tm_hour, tmp->tm_min, tmp->tm_sec);
        writeb(bin2bcd(tmp->tm_year % 100), &rtc->year);
        writeb(bin2bcd(tmp->tm_mon), &rtc->month);
 
@@ -75,6 +97,11 @@ int rtc_set(struct rtc_time *tmp)
        writeb(bin2bcd(tmp->tm_hour), &rtc->hours);
        writeb(bin2bcd(tmp->tm_min), &rtc->minutes);
        writeb(bin2bcd(tmp->tm_sec), &rtc->second);
+
+       debug("Set DATE: %4d-%02d-%02d (wday=%d)  TIME: %2d:%02d:%02d\n",
+             tmp->tm_year, tmp->tm_mon, tmp->tm_mday, tmp->tm_wday,
+             tmp->tm_hour, tmp->tm_min, tmp->tm_sec);
+
        return 0;
 }
 
-- 
2.17.1