Date:   Mon, 1 Jun 2020 14:41:20 +0100
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Tomasz Duszynski <tomasz.duszynski@...akon.com>
CC:     Jonathan Cameron <jic23@...nel.org>, <linux-iio@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <robh+dt@...nel.org>, <andy.shevchenko@...il.com>,
        <pmeerw@...erw.net>
Subject: Re: [PATCH v2 1/4] iio: chemical: scd30: add core driver

...

> > > > > +
> > > > > +	return ret;
> > > > > +}
> > > > > +
> > > > > +int scd30_probe(struct device *dev, int irq, const char *name, void *priv,
> > > > > +		scd30_command_t command)
> > > > > +{
> > > > > +	static const unsigned long scd30_scan_masks[] = { 0x07, 0x00 };
> > > > > +	struct scd30_state *state;
> > > > > +	struct iio_dev *indio_dev;
> > > > > +	int ret;
> > > > > +	u16 val;
> > > > > +
> > > > > +	indio_dev = devm_iio_device_alloc(dev, sizeof(*state));
> > > > > +	if (!indio_dev)
> > > > > +		return -ENOMEM;
> > > > > +
> > > > > +	state = iio_priv(indio_dev);
> > > > > +	state->dev = dev;  
> > > >
> > > > Doesn't seem to be used.
> > > >  
> > > > > +	state->priv = priv;  
> > > >
> > > > What's this for?  At least at first glance I can't find it being used
> > > > anywhere.
> > > >  
> > > > > +	state->irq = irq;
> > > > > +	state->pressure_comp = SCD30_PRESSURE_COMP_DEFAULT;
> > > > > +	state->meas_interval = SCD30_MEAS_INTERVAL_DEFAULT;
> > > > > +	state->command = command;
> > > > > +	mutex_init(&state->lock);
> > > > > +	init_completion(&state->meas_ready);
> > > > > +
> > > > > +	dev_set_drvdata(dev, indio_dev);
> > > > > +
> > > > > +	indio_dev->dev.parent = dev;  
> > > >
> > > > Side note that there is a series moving this into the core under revision at
> > > > the moment.  Hopefully I'll remember to fix this up when applying your patch
> > > > if that one has gone in ahead of it.
> > > >  
> > > > > +	indio_dev->info = &scd30_info;
> > > > > +	indio_dev->name = name;
> > > > > +	indio_dev->channels = scd30_channels;
> > > > > +	indio_dev->num_channels = ARRAY_SIZE(scd30_channels);
> > > > > +	indio_dev->modes = INDIO_DIRECT_MODE;
> > > > > +	indio_dev->available_scan_masks = scd30_scan_masks;
> > > > > +
> > > > > +	state->vdd = devm_regulator_get(dev, "vdd");
> > > > > +	if (IS_ERR(state->vdd)) {
> > > > > +		if (PTR_ERR(state->vdd) == -EPROBE_DEFER)
> > > > > +			return -EPROBE_DEFER;
> > > > > +
> > > > > +		dev_err(dev, "failed to get regulator\n");
> > > > > +		return PTR_ERR(state->vdd);
> > > > > +	}
> > > > > +
> > > > > +	ret = regulator_enable(state->vdd);
> > > > > +	if (ret)
> > > > > +		return ret;
> > > > > +
> > > > > +	ret = devm_add_action_or_reset(dev, scd30_disable_regulator, state);
> > > > > +	if (ret)
> > > > > +		return ret;
> > > > > +  
> > > >
> > > > A comment here on why it makes sense to register this here.  What
> > > > started mesurement? It seems that happens well below here so
> > > > we should really call this after that start all.
> > > >  
> > >
> > > Sensor after being powered up starts in mode it was left in.
> > > Chances are it was continuous mode and we want to shut it down.  
> >
> > That's fine.  The question is why 'here' as opposed to after the below where you
> > put it into continuous mode.
> >  
> 
> Let's suppose sensor got energized and started measuring. Then without
> registering action which stops measurement we jump to device reset etc.
> 
> Now if reset failed for whatever reason (same applies to everything
> below reset) devm will gracefully unwind previous actions but sensor
> will continue doing his job. But there's no point. Better to save some
> milliaps for later.

I'm not convinced. Note that in your example, the sensor was already on.
If we never loaded the driver it would stay on.  We should
deal with only problems we have potentially created.

If reset fails, it shouldn't 'enable' the sensor hence we are just in
the same state as if the driver hadn't loaded at all.  Also if reset
fails the chance of a disable succeeding is very low.

The code is much more logical with this being done immediately after
the action to enable thing we are disabling.  So please put it down
there.



> 
> In case we have real regulator then there's no real issue because
> power gets cut off during cleanup.
> 
> Quite often though there's only a dummy one which does nothing useful
> except making regulator framework happy.
> 
> So my thinking here is that we're slightly better off registering
> scd30_stop_meas() action earlier to prevent such scenario from happening.
> 
> > >  
> > > > > +	ret = devm_add_action_or_reset(dev, scd30_stop_meas, state);
> > > > > +	if (ret)
> > > > > +		return ret;
> > > > > +
> > > > > +	ret = scd30_reset(state);
> > > > > +	if (ret) {
> > > > > +		dev_err(dev, "failed to reset device: %d\n", ret);
> > > > > +		return ret;
> > > > > +	}
> > > > > +
> > > > > +	if (state->irq > 0) {
> > > > > +		ret = scd30_setup_trigger(indio_dev);
> > > > > +		if (ret) {
> > > > > +			dev_err(dev, "failed to setup trigger: %d\n", ret);
> > > > > +			return ret;
> > > > > +		}
> > > > > +	}
> > > > > +
> > > > > +	ret = devm_iio_triggered_buffer_setup(dev, indio_dev, NULL,
> > > > > +					      scd30_trigger_handler, NULL);
> > > > > +	if (ret)
> > > > > +		return ret;
> > > > > +
> > > > > +	ret = scd30_command_read(state, CMD_FW_VERSION, &val);
> > > > > +	if (ret) {
> > > > > +		dev_err(dev, "failed to read firmware version: %d\n", ret);
> > > > > +		return ret;
> > > > > +	}
> > > > > +	dev_info(dev, "firmware version: %d.%d\n", val >> 8, (char)val);
> > > > > +
> > > > > +	ret = scd30_command_write(state, CMD_MEAS_INTERVAL,
> > > > > +				  state->meas_interval);
> > > > > +	if (ret) {
> > > > > +		dev_err(dev, "failed to set measurement interval: %d\n", ret);
> > > > > +		return ret;
> > > > > +	}
> > > > > +
> > > > > +	ret = scd30_command_write(state, CMD_START_MEAS, state->pressure_comp);
> > > > > +	if (ret) {
> > > > > +		dev_err(dev, "failed to start measurement: %d\n", ret);
> > > > > +		return ret;
> > > > > +	}
Here is where we should register that cleanup handler.

Jonathan

> > > > > +
> > > > > +	return devm_iio_device_register(dev, indio_dev);
> > > > > +}
> > > > > +EXPORT_SYMBOL(scd30_probe);
> > > > > +
> > > > > +MODULE_AUTHOR("Tomasz Duszynski <tomasz.duszynski@...akon.com>");
> > > > > +MODULE_DESCRIPTION("Sensirion SCD30 carbon dioxide sensor core driver");
> > > > > +MODULE_LICENSE("GPL v2");
> > > > > --
> > > > > 2.26.2
> > > > >  
> > > >  
> >
> >  

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