Re: [PATCH] rtc: allow rtc_read_alarm without read_alarm callback

[Philippe Schenker]

On Tue, 2023-02-14 at 23:27 +0100, alexandre.belloni@xxxxxxxxxxx wrote:
> From: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxx>
> 
> .read_alarm is not necessary to read the current alarm because it is
> recorded in the aie_timer and so rtc_read_alarm() will never call
> rtc_read_alarm_internal() which is the only function calling the
> callback.
> 
> Reported-by: Zhipeng Wang <zhipeng.wang_1@xxxxxxx>
> Reported-by: Marcel Ziswiler <marcel.ziswiler@xxxxxxxxxxx>
> Fixes: 7ae41220ef58 ("rtc: introduce features bitfield")
> Signed-off-by: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxx>

Tested-by: Philippe Schenker <philippe.schenker@xxxxxxxxxxx>

I tested on our SoMs Colibri iMX8X and Apalis iMX8

I used the variants that had i.MX 8QXP and i.MX 8QM placed. This patch
did solve the problem we currently have. I also wanted to mention that I
could not get them to run on a mainline kernel in a acceptable time-
frame so I tested on Toradex's kernel that is based on NXP's Kernel. [1]

[1]
https://git.toradex.com/cgit/linux-toradex.git/log/?h=toradex_5.15-2.1.x-imx

> ---
>  drivers/rtc/interface.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c
> index 7c30cb3c764d..499d89150afc 100644
> --- a/drivers/rtc/interface.c
> +++ b/drivers/rtc/interface.c
> @@ -392,7 +392,7 @@ int rtc_read_alarm(struct rtc_device *rtc, struct
> rtc_wkalrm *alarm)
>                 return err;
>         if (!rtc->ops) {
>                 err = -ENODEV;
> -       } else if (!test_bit(RTC_FEATURE_ALARM, rtc->features) ||
> !rtc->ops->read_alarm) {
> +       } else if (!test_bit(RTC_FEATURE_ALARM, rtc->features)) {
>                 err = -EINVAL;
>         } else {
>                 memset(alarm, 0, sizeof(struct rtc_wkalrm));