[PATCH] rtc: mpfs: Fix alarm register word order

[PATCH] rtc: mpfs: Fix alarm register word order

[Baek Kyu, Kim]

mpfs_rtc_readalarm() swaps the low and high words of the alarm time.
The RTC core reads this value during device registration to initialize
its alarm timer. This can populate the cached alarm and timer queue
with an incorrect expiry time, or leave an enabled hardware alarm out
of the timer queue if the decoded time appears to be in the past.

Read the low 32 bits from ALARM_LOWER_REG and place the masked high
11 bits from ALARM_UPPER_REG in bits 42:32. This matches the layout
used by mpfs_rtc_setalarm() and the low/high assembly in
mpfs_rtc_readtime(), so the RTC core imports the programmed alarm
time correctly during device registration.

Fixes: 0b31d703598d ("rtc: Add driver for Microchip PolarFire SoC")
Signed-off-by: Baek Kyu, Kim <pocj8ur4in@gmail.com>
---
Tested with KUnit under ARM64 QEMU using RAM-backed MMIO and the actual
MPFS RTC callbacks and RTC core registration. All ten tests pass with the
fix, including importing a preloaded alarm and checking its timer queue
entry. Four additional tests covering current-date alarms also pass.
No physical MPFS hardware or suspend/wakeup was tested.

 drivers/rtc/rtc-mpfs.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/rtc/rtc-mpfs.c b/drivers/rtc/rtc-mpfs.c
index 60596b0ea9d8..6616ca1f02c7 100644
--- a/drivers/rtc/rtc-mpfs.c
+++ b/drivers/rtc/rtc-mpfs.c
@@ -131,8 +131,8 @@ static int mpfs_rtc_readalarm(struct device *dev, struct rtc_wkalrm *alrm)
 
 	alrm->enabled = mode & MODE_WAKE_EN;
 
-	time = (u64)readl(rtcdev->base + ALARM_LOWER_REG) << 32;
-	time |= (readl(rtcdev->base + ALARM_UPPER_REG) & ALARM_UPPER_MASK);
+	time = readl(rtcdev->base + ALARM_LOWER_REG);
+	time |= ((u64)readl(rtcdev->base + ALARM_UPPER_REG) & ALARM_UPPER_MASK) << 32;
 	rtc_time64_to_tm(time, &alrm->time);
 
 	return 0;

base-commit: 58161ead29e50d70a317ea26b472e0c7508e69da
-- 
2.55.0

Re: [PATCH] rtc: mpfs: Fix alarm register word order

[sashiko-bot]

> mpfs_rtc_readalarm() swaps the low and high words of the alarm time.
> The RTC core reads this value during device registration to initialize
> its alarm timer. This can populate the cached alarm and timer queue
> with an incorrect expiry time, or leave an enabled hardware alarm out
> of the timer queue if the decoded time appears to be in the past.
> 
> Read the low 32 bits from ALARM_LOWER_REG and place the masked high
> 11 bits from ALARM_UPPER_REG in bits 42:32. This matches the layout
> used by mpfs_rtc_setalarm() and the low/high assembly in
> mpfs_rtc_readtime(), so the RTC core imports the programmed alarm
> time correctly during device registration.
> 
> Fixes: 0b31d703598d ("rtc: Add driver for Microchip PolarFire SoC")
> Signed-off-by: Baek Kyu, Kim <pocj8ur4in@gmail.com>

Sashiko has reviewed this patch and found no issues.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261019151024.2232338-1-pocj8ur4in@gmail.com?part=1