Re: [PATCH v4 03/15] rtc: rzn1: Fix weekday underflow when alarm crosses month boundary

[Wolfram Sang]

On Wed, Aug 19, 2026 at 11:39:14AM +0100, Prabhakar wrote:
> From: Lad Prabhakar <prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx>
> 
> rzn1_rtc_set_alarm() calculates the alarm weekday from the difference
> between the alarm day and the current day of the month. When the alarm
> crosses a month boundary, this difference can become negative. Since
> days_ahead is unsigned, it underflows and results in an incorrect
> weekday being programmed into RZN1_RTC_ALW.
> 
> The RTC core already provides a fully populated struct rtc_time for
> the alarm, including the correct tm_wday. Use tm->tm_wday directly
> instead of recalculating the weekday from the day-of-month.
> 
> This avoids the underflow and ensures alarms scheduled across a month
> boundary use the correct weekday.
> 
> Fixes: b5ad1bf00d2c4 ("rtc: rzn1: Add alarm support")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx>

Suggested-by: Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx>

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