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

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Message-ID: <2023061214170504ac9f0b@mail.local>
Date:   Mon, 12 Jun 2023 16:17:05 +0200
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
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 14:30:18+0200, Rasmus Villemoes wrote:
> On 12/06/2023 13.30, Rasmus Villemoes wrote:
> 
> > diff --git a/drivers/rtc/rtc-isl12022.c b/drivers/rtc/rtc-isl12022.c
> > index 1b6659a9b33a..690dbb446d1a 100644
> > --- a/drivers/rtc/rtc-isl12022.c
> > +++ b/drivers/rtc/rtc-isl12022.c
> > @@ -280,8 +280,25 @@ static void isl12022_set_trip_levels(struct device *dev)
> >  	mask = ISL12022_REG_VB85_MASK | ISL12022_REG_VB75_MASK;
> >  
> >  	ret = regmap_update_bits(regmap, ISL12022_REG_PWR_VBAT, mask, val);
> > -	if (ret)
> > +	if (ret) {
> >  		dev_warn(dev, "unable to set battery alarm levels: %d\n", ret);
> > +		return;
> > +	}
> > +
> > +	ret = regmap_write_bits(regmap, ISL12022_REG_BETA,
> > +				ISL12022_BETA_TSE, ISL12022_BETA_TSE);
> > +	if (ret) {
> > +		dev_warn(dev, "unable to trigger battery level detection: %d\n", ret);
> > +		return;
> > +	}
> > +
> > +	ret = isl12022_read_sr(regmap);
> 
> 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.

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