[PATCH v5 04/17] rtc: rzn1: Handle unset alarm weekday in rzn1_rtc_read_alarm

[Prabhakar]

From: Lad Prabhakar <prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx>

RZN1_RTC_ALW is a weekday bitmask where bit N represents weekday N.
When no alarm has been configured, the register has its power-on-reset
value of zero.

rzn1_rtc_read_alarm() uses fls() to convert the weekday bitmask into a
weekday number. When RZN1_RTC_ALW is zero, fls(0) returns zero and
fls(wday) - 1 evaluates to -1. This invalid weekday is then used to
calculate the alarm date and can either leave tm_wday set to -1 or
produce a fabricated alarm date.

Treat a zero RZN1_RTC_ALW value as an unset alarm weekday and return
without calculating the alarm date. Move reading RZN1_RTC_CTL1 before
this check so that alrm->enabled is updated for both configured and
unconfigured alarms.

On a cold-booted board with no alarm configured, the following was
observed before the fix:

    root@rzn2h-evk:~# cat /proc/driver/rtc
    rtc_time        : 00:00:19
    rtc_date        : 2000-01-01
    alrm_time       : 00:00:00
    alrm_date       : 2000-01-07
    alarm_IRQ       : no
    alrm_pending    : no
    update IRQ enabled      : no
    periodic IRQ enabled    : no
    periodic IRQ frequency  : 1
    max user IRQ frequency  : 64
    24hr            : yes

After the fix:

    root@rzn2h-evk:~# cat /proc/driver/rtc
    rtc_time        : 00:00:25
    rtc_date        : 2000-01-01
    alrm_time       : 00:00:00
    alrm_date       : 2000-01-01
    alarm_IRQ       : no
    alrm_pending    : no
    update IRQ enabled      : no
    periodic IRQ enabled    : no
    periodic IRQ frequency  : 1
    max user IRQ frequency  : 64
    24hr            : yes

Fixes: b5ad1bf00d2c4 ("rtc: rzn1: Add alarm support")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx>
---
v4->v5:
- New patch
---
 drivers/rtc/rtc-rzn1.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/rtc/rtc-rzn1.c b/drivers/rtc/rtc-rzn1.c
index 8c70dbf8c7ec..e0fdb591ba91 100644
--- a/drivers/rtc/rtc-rzn1.c
+++ b/drivers/rtc/rtc-rzn1.c
@@ -234,13 +234,24 @@ static int rzn1_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
 	if (ret)
 		return ret;
 
+	ctl1 = readl(rtc->base + RZN1_RTC_CTL1);
+	alrm->enabled = !!(ctl1 & (RZN1_RTC_CTL1_ALME | RZN1_RTC_CTL1_1SE));
+
 	min = readl(rtc->base + RZN1_RTC_ALM);
 	hour = readl(rtc->base + RZN1_RTC_ALH);
-	wday = readl(rtc->base + RZN1_RTC_ALW);
 
 	tm->tm_sec = 0;
 	tm->tm_min = bcd2bin(min);
 	tm->tm_hour = bcd2bin(hour);
+
+	/*
+	 * If wday is zero, no bit is set in RZN1_RTC_ALW. This is the
+	 * register's power-on reset value.
+	 */
+	wday = readl(rtc->base + RZN1_RTC_ALW);
+	if (!wday)
+		return 0;
+
 	delta_days = ((fls(wday) - 1) - tm->tm_wday + 7) % 7;
 	tm->tm_wday = fls(wday) - 1;
 
@@ -249,9 +260,6 @@ static int rzn1_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
 		rtc_time64_to_tm(alarm, tm);
 	}
 
-	ctl1 = readl(rtc->base + RZN1_RTC_CTL1);
-	alrm->enabled = !!(ctl1 & (RZN1_RTC_CTL1_ALME | RZN1_RTC_CTL1_1SE));
-
 	return 0;
 }
 
-- 
2.43.0