Re: [PATCH v4 2/3] iio: add MEMSensing MSA311 3-axis accelerometer driver

[Christophe JAILLET]

Le 03/08/2022 à 20:39, Dmitry Rokosov a écrit :
> Hello Christophe,
>
> Thank you for quick review
>
> On Wed, Aug 03, 2022 at 08:11:05PM +0200, Christophe JAILLET wrote:
> > Le 03/08/2022 à 15:11, Dmitry Rokosov a écrit :
> > > MSA311 is a tri-axial, low-g accelerometer with I2C digital output for
> > > sensitivity consumer applications. It has dynamic user-selectable full
> > > scales range of +-2g/+-4g/+-8g/+-16g and allows acceleration measurements
> > > with output data rates from 1Hz to 1000Hz.
> > >
> > > Spec: https://cdn-shop.adafruit.com/product-files/5309/MSA311-V1.1-ENG.pdf
> > >
> > > This driver supports following MSA311 features:
> > >       - IIO interface
> > >       - Different power modes: NORMAL and SUSPEND (using pm_runtime)
> > >       - ODR (Output Data Rate) selection
> > >       - Scale and samp_freq selection
> > >       - IIO triggered buffer, IIO reg access
> > >       - NEW_DATA interrupt + trigger
> > >
> > > Below features to be done:
> > >       - Motion Events: ACTIVE, TAP, ORIENT, FREEFALL
> > >       - Low Power mode
> > >
> > > Signed-off-by: Dmitry Rokosov <ddrokosov-i4r8oA+eLlH99rHkP+FxIw@xxxxxxxxxxxxxxxx>
> > > ---
> > >    MAINTAINERS                |    6 +
> > >    drivers/iio/accel/Kconfig  |   13 +
> > >    drivers/iio/accel/Makefile |    2 +
> > >    drivers/iio/accel/msa311.c | 1323 ++++++++++++++++++++++++++++++++++++
> > >    4 files changed, 1344 insertions(+)
> > >    create mode 100644 drivers/iio/accel/msa311.c
> >
> > Hi,
> > a few nits below.
> >
> > [...]
> >
> > > +static int msa311_check_partid(struct msa311_priv *msa311)
> > > +{
> > > +	struct device *dev = msa311->dev;
> > > +	unsigned int partid;
> > > +	int err;
> > > +
> > > +	err = regmap_read(msa311->regs, MSA311_PARTID_REG, &partid);
> > > +	if (err)
> > > +		return dev_err_probe(dev, err,
> > > +				     "failed to read partid (%d)\n", err);
> >
> > No need for "(%d)" and err.
>
> Do you mean for all dev_err() calls? I think sometimes it's helpful to
> know the actual error value got from external API, isn't? Could you please
> explain your point if possible?

No, my comment is only for dev_err_probe() function.
Having ret for dev_err() calls is fine.

See: https://elixir.bootlin.com/linux/v5.19/source/drivers/base/core.c#L4732

dev_err_probe() already has a "error %pe:..., ERR_PTR(err)"
This means that if ret = -ENOMEM:
   "(%d)"       --> "(-12)"
   "error %pe:" --> "error -ENOMEM:"

So there is no real need to duplicate the error code in the message 
itself, it is already displayed in a human readable manner.

What your code does would result in:
   "error -ENOMEM: failed to read partid (-12)\n"

> > > +
> > > +	if (partid == MSA311_WHO_AM_I)
> > > +		dev_dbg(dev, "found MSA311 compatible chip[%#x]\n", partid);
> > > +	else
> > > +		dev_warn(dev, "invalid partid (%#x), expected (%#x)\n",
> > > +			 partid, MSA311_WHO_AM_I);
> > > +
> > > +	return 0;
> > > +}
> >
> > [...]
> >
> > > +static int msa311_probe(struct i2c_client *i2c)
> > > +{
> > > +	struct device *dev = &i2c->dev;
> > > +	struct msa311_priv *msa311;
> > > +	struct iio_dev *indio_dev;
> > > +	int err;
> > > +
> > > +	indio_dev = devm_iio_device_alloc(dev, sizeof(*msa311));
> > > +	if (!indio_dev)
> > > +		return dev_err_probe(dev, -ENOMEM,
> > > +				     "iio device allocation failed\n");
> > > +
> > > +	msa311 = iio_priv(indio_dev);
> > > +	msa311->dev = dev;
> > > +	i2c_set_clientdata(i2c, indio_dev);
> > > +
> > > +	err = msa311_regmap_init(msa311);
> > > +	if (err)
> > > +		return err;
> > > +
> > > +	mutex_init(&msa311->lock);
> > > +
> > > +	msa311->vdd = devm_regulator_get_optional(dev, "vdd");
> > > +	if (IS_ERR(msa311->vdd)) {
> > > +		err = PTR_ERR(msa311->vdd);
> > > +		if (err == -ENODEV)
> > > +			msa311->vdd = NULL;
> > > +		else
> > > +			return dev_err_probe(dev, PTR_ERR(msa311->vdd),
> > > +					     "cannot get vdd supply\n");
> > > +	}
> > > +
> > > +	if (msa311->vdd) {
> > > +		err = regulator_enable(msa311->vdd);
> > > +		if (err)
> > > +			return dev_err_probe(dev, err,
> > > +					     "cannot enable vdd supply\n");
> > > +
> > > +		err = devm_add_action_or_reset(dev, msa311_vdd_disable,
> > > +					       msa311->vdd);
> > > +		if (err) {
> > > +			regulator_disable(msa311->vdd);
> >
> > Double regulator_disable(), because of the _or_reset()?
>
> Yep. If devm_add_action_or_reset() returns an error, we will not
> call regulator_disable() by devm subsystem. It means, we have to
> call it directly.

No.

See 
https://elixir.bootlin.com/linux/v5.19/source/include/linux/device.h#L249

If devm_add_action_or_reset() fails, "action" is called. This is the 
meaning of the _or_reset suffix.

So here, msa311_vdd_disable() would be called and this function is:

+static void msa311_vdd_disable(void *vdd)
+{
+	regulator_disable(vdd);
+}

and "vdd" will be the value of "msa311->vdd"

So, unless I missed something obvious, your code will call twice 
regulator_disable(msa311->vdd).

One in devm_add_action_or_reset() and one explicitly after the "if (err)"


Hoping I'm clear and that I didn't miss something obvious.

CJ

> > > +			return dev_err_probe(dev, err,
> > > +					     "cannot add vdd disable action\n");
> > > +		}
> > > +	}
> > > +
> > > +	err = msa311_check_partid(msa311);
> > > +	if (err)
> > > +		return err;
> > > +
> > > +	err = msa311_soft_reset(msa311);
> > > +	if (err)
> > > +		return err;
> > > +
> > > +	err = msa311_set_pwr_mode(msa311, MSA311_PWR_MODE_NORMAL);
> > > +	if (err)
> > > +		return dev_err_probe(dev, err,
> > > +				     "failed to power on device (%d)\n", err);
> >
> > No need for "(%d)" and err
>
> Asked for the clarification above.
>
> > CJ