linux-kernel - Re: [PATCH] rtc: cros-ec: return -ETIME when refused to set alarms in the past

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Message-ID: <20180226183727.GC225858@rodete-desktop-imager.corp.google.com>
Date:   Mon, 26 Feb 2018 10:37:28 -0800
From:   Brian Norris <briannorris@...omium.org>
To:     Jeffy Chen <jeffy.chen@...k-chips.com>
Cc:     linux-kernel@...r.kernel.org, zyw@...k-chips.com,
        briannorris@...gle.com, dianders@...gle.com, jwerner@...omium.org,
        linux-rtc@...r.kernel.org,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Alessandro Zummo <a.zummo@...ertech.it>
Subject: Re: [PATCH] rtc: cros-ec: return -ETIME when refused to set alarms
 in the past

One last note:

On Sun, Feb 25, 2018 at 04:18:02PM +0800, Jeffy Chen wrote:
> We have a check in __rtc_set_alarm() to return -ETIME when the alarm
> is in the past.
> 
> Since accessing a Chrome OS EC based rtc is a slow operation, we should
> do that check again inside of the EC rtc driver's .set_alarm() callback.
> 
> Signed-off-by: Jeffy Chen <jeffy.chen@...k-chips.com>
> ---
> 
>  drivers/rtc/rtc-cros-ec.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/rtc/rtc-cros-ec.c b/drivers/rtc/rtc-cros-ec.c
> index f0ea6899c731..ee0062e2d222 100644
> --- a/drivers/rtc/rtc-cros-ec.c
> +++ b/drivers/rtc/rtc-cros-ec.c
> @@ -188,6 +188,10 @@ static int cros_ec_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
>  	if (alarm_time < 0 || alarm_time > U32_MAX)
>  		return -EINVAL;
>  
> +	/* Don't set an alarm in the past. */
> +	if ((u32)alarm_time <= current_time)
> +		return -ETIME;
> +
>  	if (!alrm->enabled) {
>  		/*
>  		 * If the alarm is being disabled, send an alarm
> @@ -196,11 +200,7 @@ static int cros_ec_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
>  		alarm_offset = EC_RTC_ALARM_CLEAR;
>  		cros_ec_rtc->saved_alarm = (u32)alarm_time;
>  	} else {
> -		/* Don't set an alarm in the past. */
> -		if ((u32)alarm_time < current_time)

It's probably worth noting in the commit message that you're also fixing
the case where 'alarm_time == current_time'; in the current driver
source, it *looks* like you're setting a 0-second alarm. But in fact, 0
means EC_RTC_ALARM_CLEAR, which would disable the alarm. So you are
(correctly) returning -ETIME in that case.

Brian

> -			alarm_offset = EC_RTC_ALARM_CLEAR;
> -		else
> -			alarm_offset = (u32)alarm_time - current_time;
> +		alarm_offset = (u32)alarm_time - current_time;
>  	}
>  
>  	ret = cros_ec_rtc_set(cros_ec, EC_CMD_RTC_SET_ALARM, alarm_offset);
> -- 
> 2.11.0
> 
>