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

Wolfram Sang <[email protected]> Fri, 21 Aug 2026 17:08:58 +0200

Newsgroups	org.kernel.vger.linux-rtc,org.kernel.vger.linux-devicetree,org.kernel.vger.linux-kernel,org.kernel.vger.linux-renesas-soc,org.kernel.vger.stable
Message-ID	<aohqChLVqwiTpICo@ninjato>

On Fri, Aug 21, 2026 at 02:55:55PM +0100, Prabhakar wrote:
> From: Lad Prabhakar <[email protected]>
> 
> 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

The output of the tests could be dropped IMO, but I'll leave this for
the RTC maintainers.

> Fixes: b5ad1bf00d2c4 ("rtc: rzn1: Add alarm support")
> Cc: [email protected]
> Signed-off-by: Lad Prabhakar <[email protected]>

Other than that:

Reviewed-by: Wolfram Sang <[email protected]>
Tested-by: Wolfram Sang <[email protected]>

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