Blackfin RTC driver: the frequency function is in units of Hz, not units of...

Blackfin RTC driver: the frequency function is in units of Hz, not units of seconds, so lock our driver down to 1 Hz
Signed-off-by: NMike Frysinger <michael.frysinger@analog.com>
Signed-off-by: NBryan Wu <bryan.wu@analog.com>
Acked-by: NAlessandro Zummo <alessandro.zummo@towertech.it>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/rtc/rtc-bfin.c

@@ -72,7 +72,7 @@ struct bfin_rtc {
 #define SEC_BITS_OFF    0
 
 /* Some helper functions to convert between the common RTC notion of time
- * and the internal Blackfin notion that is stored in 32bits.
+ * and the internal Blackfin notion that is encoded in 32bits.
  */
 static inline u32 rtc_time_to_bfin(unsigned long now)
 {
@@ -112,6 +112,11 @@ static inline void rtc_bfin_to_tm(u32 rtc_bfin, struct rtc_time *tm)
  * If anyone can point out the obvious solution here, i'm listening :).  This
  * shouldn't be an issue on an SMP or preempt system as this function should
  * only be called with the rtc lock held.
+ *
+ * Other options:
+ *  - disable PREN so the sync happens at 32.768kHZ ... but this changes the
+ *    inc rate for all RTC registers from 1HZ to 32.768kHZ ...
+ *  - use the write complete IRQ
  */
 static void rtc_bfin_sync_pending(void)
 {
@@ -356,12 +361,18 @@ static int bfin_rtc_proc(struct device *dev, struct seq_file *seq)
 	return 0;
 }
 
+/**
+ *	bfin_irq_set_freq - make sure hardware supports requested freq
+ *	@dev: pointer to RTC device structure
+ *	@freq: requested frequency rate
+ *
+ *	The Blackfin RTC can only generate periodic events at 1 per
+ *	second (1 Hz), so reject any attempt at changing it.
+ */
 static int bfin_irq_set_freq(struct device *dev, int freq)
 {
-	struct bfin_rtc *rtc = dev_get_drvdata(dev);
 	stampit();
-	rtc->rtc_dev->irq_freq = freq;
-	return 0;
+	return -ENOTTY;
 }
 
 static struct rtc_class_ops bfin_rtc_ops = {
@@ -394,14 +405,13 @@ static int __devinit bfin_rtc_probe(struct platform_device *pdev)
 		ret = PTR_ERR(rtc->rtc_dev);
 		goto err;
 	}
-	rtc->rtc_dev->irq_freq = 0;
-	rtc->rtc_dev->max_user_freq = (2 << 16); /* stopwatch is an unsigned 16 bit reg */
+	rtc->rtc_dev->irq_freq = 1;
 
 	platform_set_drvdata(pdev, rtc);
 
 	return 0;
 
-err:
+ err:
 	kfree(rtc);
 	return ret;
 }