linux-kernel - Re: [RESEND PATCH v3] rtc: cros-ec: return -ETIME when refused to set alarms in the past

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Message-ID: <20180306145602.GA3035@piout.net>
Date:   Tue, 6 Mar 2018 15:56:02 +0100
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
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, Alessandro Zummo <a.zummo@...ertech.it>
Subject: Re: [RESEND PATCH v3] rtc: cros-ec: return -ETIME when refused to
 set alarms in the past

On 27/02/2018 at 10:50:03 +0800, Jeffy Chen wrote:
> Since accessing a Chrome OS EC based rtc is a slow operation, there is a
> race window where if the alarm is set for the next second and the second
> ticks over right before calculating the alarm offset.
> 
> In this case the current driver is setting a 0-second alarm, which would
> be considered as disabling alarms by the EC(EC_RTC_ALARM_CLEAR).
> 
> This breaks, e.g., hwclock which relies on RTC_UIE_ON ->
> rtc_update_irq_enable(), which sets a 1-second alarm and expects it to
> fire an interrupt.
> 
> So return -ETIME when the alarm is in the past, follow __rtc_set_alarm().
> 
> Signed-off-by: Jeffy Chen <jeffy.chen@...k-chips.com>
> ---
> 
> Changes in v3:
> Fix alarm time comparing.
> 
> Changes in v2:
> Rewrite commit message as Brian suggested.
> Check alarm time only when that alarm is enabled.
> 
>  drivers/rtc/rtc-cros-ec.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
Applied, thanks.

-- 
Alexandre Belloni, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com