linux-kernel - Re: [PATCH] selftests/rtc: continuously read RTC in a loop for 30s

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Message-ID: <6d8f500d-0ee0-3e27-dfdf-e8c0a34880e5@linuxfoundation.org>
Date:   Fri, 25 Feb 2022 13:56:25 -0700
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     Mateusz Jończyk <mat.jonczyk@...pl>,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-rtc@...r.kernel.org
Cc:     Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Shuah Khan <shuah@...nel.org>,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH] selftests/rtc: continuously read RTC in a loop for 30s

On 2/19/22 12:27 AM, Mateusz Jończyk wrote:
> Some problems with reading the RTC time may happen rarely, for example
> while the RTC is updating. So read the RTC many times to catch these
> problems. For example, a previous attempt for my
> commit ea6fa4961aab ("rtc: mc146818-lib: fix RTC presence check")
> was incorrect and would have triggered this selftest.
> 
> To avoid the risk of damaging the hardware, wait 11ms before consecutive
> reads.
> 
> In rtc_time_to_timestamp I copied values manually instead of casting -
> just to be on the safe side. The 11ms wait period was chosen so that it is
> not a divisor of 1000ms.
> 
> Signed-off-by: Mateusz Jończyk <mat.jonczyk@...pl>
> Cc: Alessandro Zummo <a.zummo@...ertech.it>
> Cc: Alexandre Belloni <alexandre.belloni@...tlin.com>
> Cc: Shuah Khan <shuah@...nel.org>
> ---
> 
> Also, before
> commit cdedc45c579f ("rtc: cmos: avoid UIP when reading alarm time")
> reading the RTC alarm time during RTC update produced incorrect results
> on many Intel platforms. Preparing a similar selftest for this case
> would be more difficult, though, because the RTC alarm time is cached by
> the kernel. Direct access would have to be exposed somehow, for example
> in debugfs. I may prepare a patch for it in the future.
> ---

Looks good to me. We end up tweaking the timeout=210 in settings every
now and then. Not sure how we can avoid adjusting it as we find problems.

I will apply this in for Linux 5.18-rc1

thanks,
-- Shuah