linux-kernel - Re: [PATCH 6/8] rtc: isl12022: trigger battery level detection during probe

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Date:   Tue, 13 Jun 2023 09:51:01 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc:     Alessandro Zummo <a.zummo@...ertech.it>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        devicetree@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>, linux-rtc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/8] rtc: isl12022: trigger battery level detection during
 probe

On 12/06/2023 16.17, Alexandre Belloni wrote:
> On 12/06/2023 14:30:18+0200, Rasmus Villemoes wrote:

>> So testing this a bit more thoroughly reveals that the LBAT85/LBAT75
>> bits do not get updated immediately after the TSE bit is set; one needs
>> to wait a little before the battery voltage detection is done and the SR
>> bits updated. Unfortunately, the data sheet doesn't say anything about
>> how long that might be or if there's some busy bit one could look at;
>> all it says is actually exactly what I've done above:
>>
>>   The battery level monitor is not functional in battery backup
>>   mode. In order to read the monitor bits after powering up VDD,
>>   instigate a battery level measurement by setting the TSE bit to
>>   "1" (BETA register), and then read the bits.
>>
>> IOW, please don't apply this patch until I figure out how to do this
>> properly.
>>
> 
> The datasheet states 22ms for the temperature conversion so I would
> expect it takes about that time.

It's most likely much shorter than that - if I just busy-read SR until
the LBAT bits are clear, that takes no more than 2ms, and the final read
of SR still has the BUSY bit set, indicating a temp conversion being
(still) in progress. But I'd prefer to have Renesas provide the proper
value rather than using some seems-to-work-on-my-desk. But but, it's
probably moot, see other reply.

Rasmus