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

From: Rasmus Villemoes <linux@rasmusvillemoes.dk>
To: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	devicetree@vger.kernel.org, Rob Herring <robh+dt@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Conor Dooley <conor+dt@kernel.org>,
	linux-rtc@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 6/8] rtc: isl12022: trigger battery level detection during probe
Date: Tue, 13 Jun 2023 09:51:01 +0200	[thread overview]
Message-ID: <919df40e-2f8a-1ad9-7c2e-9ba9fe1a481a@rasmusvillemoes.dk> (raw)
In-Reply-To: <2023061214170504ac9f0b@mail.local>

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