rtc: s5m: use shorter time of register update

Set the time needed for updating alarm and time registers to 0.45 ms.
The default is 7.32 ms which is too long and leads to warnings when
setting alarm or time:

	s5m-rtc: waiting for UDR update, reached max number of retries
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Lee Jones <lee.jones@linaro.org>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Sangbeom Kim <sbkim73@samsung.com>
Cc: Samuel Ortiz <sameo@linux.intel.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/rtc/rtc-s5m.c

@@ -519,6 +519,13 @@ static int s5m8767_rtc_init_reg(struct s5m_rtc_info *info)
 	u8 data[2];
 	int ret;
 
+	/* UDR update time. Default of 7.32 ms is too long. */
+	ret = regmap_update_bits(info->regmap, S5M_RTC_UDR_CON,
+			S5M_RTC_UDR_T_MASK, S5M_RTC_UDR_T_450_US);
+	if (ret < 0)
+		dev_err(info->dev, "%s: fail to change UDR time: %d\n",
+				__func__, ret);
+
 	/* Set RTC control register : Binary mode, 24hour mode */
 	data[0] = (1 << BCD_EN_SHIFT) | (1 << MODEL24_SHIFT);
 	data[1] = (0 << BCD_EN_SHIFT) | (1 << MODEL24_SHIFT);

include/linux/mfd/samsung/rtc.h

@@ -111,6 +111,16 @@ enum s2mps_rtc_reg {
 #define RTC_TCON_MASK		(1 << RTC_TCON_SHIFT)
 #define S5M_RTC_TIME_EN_SHIFT	3
 #define S5M_RTC_TIME_EN_MASK	(1 << S5M_RTC_TIME_EN_SHIFT)
+/*
+ * UDR_T field in S5M_RTC_UDR_CON register determines the time needed
+ * for updating alarm and time registers. Default is 7.32 ms.
+ */
+#define S5M_RTC_UDR_T_SHIFT	6
+#define S5M_RTC_UDR_T_MASK	(0x3 << S5M_RTC_UDR_T_SHIFT)
+#define S5M_RTC_UDR_T_7320_US	(0x0 << S5M_RTC_UDR_T_SHIFT)
+#define S5M_RTC_UDR_T_1830_US	(0x1 << S5M_RTC_UDR_T_SHIFT)
+#define S5M_RTC_UDR_T_3660_US	(0x2 << S5M_RTC_UDR_T_SHIFT)
+#define S5M_RTC_UDR_T_450_US	(0x3 << S5M_RTC_UDR_T_SHIFT)
 
 /* RTC Hour register */
 #define HOUR_PM_SHIFT		6