From: Jan Kiszka <jan.kiszka@siemens.com>
To: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>,
linux-rtc@vger.kernel.org,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] rtc: pcf-8563: Report previously detected low-voltage via RTC_VL_BACKUP_LOW
Date: Sun, 11 Jun 2023 15:38:04 +0200 [thread overview]
Message-ID: <1d532c45-ee33-9729-f0ac-b59c2bec8d7d@siemens.com> (raw)
In-Reply-To: <20230610083135e40dd2f6@mail.local>
On 10.06.23 10:31, Alexandre Belloni wrote:
> Hello Jan,
>
> On 09/06/2023 23:04:12+0200, Jan Kiszka wrote:
>> From: Jan Kiszka <jan.kiszka@siemens.com>
>>
>> The VL bit in the seconds register remains set only until seconds are
>> written under main power. As this often happens during boot-up after
>> picking up a network time, make sure to preserve the low battery state
>> across this, caching it and returning it via the RTC_VL_BACKUP_LOW bit.
>>
>> To permit userspace clearing this state during runtime, also implement
>> RTC_VL_CLR that works against the cached state.
>>
>> This is emulating RTCs which have a battery voltage check that works
>> under main power as well.
>>
>
> Emulating doesn't work well and I deliberately chose to not implement
> it. For example, in your scenario, if you boot twice without using
> VL_READ, you anyway have lost the information. This makes emulating
> unreliabl. The fix you need is in userspace where you have to ensure you
> read the status before setting the time.
Then let's make sure the bit is also set in the hardware register. Then
also the reboot issue (which is practically a minor one) is solved. The
current situation is far from optimal.
Jan
--
Siemens AG, Technology
Competence Center Embedded Linux
next prev parent reply other threads:[~2023-06-11 13:38 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-09 21:04 [PATCH] rtc: pcf-8563: Report previously detected low-voltage via RTC_VL_BACKUP_LOW Jan Kiszka
2023-06-10 8:31 ` Alexandre Belloni
2023-06-11 13:38 ` Jan Kiszka [this message]
2023-06-11 15:11 ` Alexandre Belloni
2023-06-11 16:28 ` Jan Kiszka
2023-06-11 22:16 ` Alexandre Belloni
2023-06-12 6:49 ` Jan Kiszka
2023-07-11 7:27 ` Jan Kiszka
2023-07-11 20:54 ` Alexandre Belloni
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