linux-kernel - Re: [PATCH 03/10] iio: accel: BMA220 migrate to regmap API

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Message-ID: <aL5NCVh9WylPhZ1O@sunspire>
Date: Mon, 8 Sep 2025 06:27:05 +0300
From: Petre Rodan <petre.rodan@...dimension.ro>
To: Jonathan Cameron <jic23@...nel.org>
Cc: linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
	David Lechner <dlechner@...libre.com>,
	Nuno S?? <nuno.sa@...log.com>, Andy Shevchenko <andy@...nel.org>
Subject: Re: [PATCH 03/10] iio: accel: BMA220 migrate to regmap API

On Sun, Sep 07, 2025 at 01:45:06PM +0100, Jonathan Cameron wrote:
> > +static int bma220_reset(struct bma220_data *data, bool up)
> >  {
> > +	int i, ret;
> > +	unsigned int val;
> > +	guard(mutex)(&data->lock);
> > 
> > +	/**
> > +	 * The chip can be reset by a simple register read.
> > +	 * We need up to 2 register reads of the softreset register
> 
> May need?  Given you return early if the first one succeeds. If you actually
> need two drop the loop and only check values on second read.
> 
> > +	 * to make sure that the device is in the desired state.
> > +	 */
> > +	for (i = 0; i < 2; i++) {
> > +		ret = regmap_read(data->regmap, BMA220_REG_SOFTRESET, &val);
> > +		if (ret < 0)
> > +			return ret;

I'm not sure how eloquently I can explain this. the sensor can be in

sleep state / non-sleep state
reset state / non-reset state
(these overlap)

the sensor toggles between these states when the master reads the suspend and
the soft_reset registers respectively.
based on the value read one can tell what was the previous state the sensor was in.

bma220_init() simply places the sensor in the non-sleep AND non-reset modes (and
resets all configuration registers so that we start from a known initial condition)

'may need' is used because the sensor might have been left in an unexpected mode
in the previous session.
we need at most two reads of a register to make sure bma220 ends up in the state we need.

best regards,
peter

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