linux-kernel - Re: [PATCH 5/5] rtc: sc27xx: Always read normal alarm when registering RTC device

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Message-ID: <20181025003456.GB2737@piout.net>
Date:   Thu, 25 Oct 2018 02:34:56 +0200
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Baolin Wang <baolin.wang@...aro.org>
Cc:     a.zummo@...ertech.it, broonie@...nel.org,
        linux-rtc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] rtc: sc27xx: Always read normal alarm when
 registering RTC device

Hello,

On 18/10/2018 16:52:30+0800, Baolin Wang wrote:
> When registering one RTC device, it will check to see if there is an
> alarm already set in RTC hardware by reading RTC alarm, at this time
> we should always read the normal alarm put in always-on region by
> checking the rtc->registered flag.
> 
> Signed-off-by: Baolin Wang <baolin.wang@...aro.org>
> ---
>  drivers/rtc/rtc-sc27xx.c |    8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/rtc/rtc-sc27xx.c b/drivers/rtc/rtc-sc27xx.c
> index 72bb002..b4eb3b3 100644
> --- a/drivers/rtc/rtc-sc27xx.c
> +++ b/drivers/rtc/rtc-sc27xx.c
> @@ -415,10 +415,14 @@ static int sprd_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
>  	u32 val;
>  
>  	/*
> -	 * If aie_timer is enabled, we should get the normal alarm time.
> +	 * Before RTC device is registered, it will check to see if there is an
> +	 * alarm already set in RTC hardware, and we always read the normal
> +	 * alarm at this time.
> +	 *
> +	 * Or if aie_timer is enabled, we should get the normal alarm time.
>  	 * Otherwise we should get auxiliary alarm time.
>  	 */
> -	if (rtc->rtc && rtc->rtc->aie_timer.enabled == 0)
> +	if (rtc->rtc && rtc->rtc->registered && rtc->rtc->aie_timer.enabled == 0)

Note that the driver should not access rtc->registered and
rtc->aie_timer.enabled and this is a bit fragile.
But, on the other hand, I currently don't have anything better to
suggest. I was also planning to add an in-kernel API for multiple alarms
but I'm not sure it will actually help in your case.

Anyway, this is applied.

-- 
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com