linux-kernel - Re: [PATCH v2 2/2] iio: (bma400) add driver for the BMA400

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Message-ID: <20191012153556.GA15972@nessie>
Date:   Sat, 12 Oct 2019 15:35:56 +0000
From:   Dan Robertson <dan@...obertson.com>
To:     Jonathan Cameron <jic23@...nel.org>
Cc:     linux-iio@...r.kernel.org,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        devicetree@...r.kernel.org, Hartmut Knaack <knaack.h@....de>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-kernel@...r.kernel.org,
        Andy Shevchenko <andy.shevchenko@...il.com>
Subject: Re: [PATCH v2 2/2] iio: (bma400) add driver for the BMA400

Thanks again everyone for the informative feedback!

On Sat, Oct 12, 2019 at 10:31:07AM +0100, Jonathan Cameron wrote:
> Apologies for not pointing this out in V1 but all new IIO bindings need
> to be in the yaml format rather than plain text.

No problem. I'll use the yaml format in v3.

On Fri, Oct 11, 2019 at 11:11:31PM -0700, Randy Dunlap wrote:
> > +config BMA400
> > +	tristate "Bosch BMA400 3-Axis Accelerometer Driver"
> > +	depends on I2C
> > +	select REGMAP
> > +	select BMA400_I2C if (I2C)
>
> Since this already has "depends on I2C", the "if (I2C)" above is not needed.
> Or maybe BMA400 alone does not depend on I2C?

Good catch. I'll remove the I2C depends from BMA400_I2C.

On Sat, Oct 12, 2019 at 10:39:54AM +0300, Andy Shevchenko wrote:
> On Sat, Oct 12, 2019 at 10:07 AM Randy Dunlap <rdunlap@...radead.org> wrote:
> > On 10/11/19 8:54 PM, Dan Robertson wrote:
>
> > > +config BMA400_I2C
> > > +     tristate
> > > +     depends on BMA400
> > > +     depends on I2C
> > > +     select REGMAP_I2C
> > > +
> >
> > The bma400_i2c driver seems to use some OF interfaces.
> > Should it also depend on OF?
>
> Please, avoid unnecessary and strict dependencies when it's limiting
> the area of use the driver.
> The driver does not depend to OF. Why to stick with OF?
>
> The actual change has to be done is to switch from
>
> > #include <linux/of.h>
>
> to
>
> #include <linux/mod_devicetable.h>

Ah! Did not know about mod_devicetable.h. I'll make this change in the next
version.

On Sat, Oct 12, 2019 at 10:40:33AM +0100, Jonathan Cameron wrote:
> > +static const struct attribute_group bma400_attrs_group = {
> > +	.attrs = bma400_attributes,
>
> No need to supply any attrs at all if the core is doing everything
> for you, so get rid of these.

Good catch.

> > +int bma400_probe(struct device *dev,
> > +		 struct regmap *regmap,
> > +		 const char *name)
>
> Try to avoid unnecessary line breaks.  There are stilly only
> so many lines on a computer monitor :)

Will do. I'll do a quick audit of the patchset for other short lines, but
please don't hesitate to point out others you may find.

> > +		/*
> > +		 * If the softreset failed, try to put the device in
> > +		 * sleep mode, but still report the error.
> > +		 */
>
> Silly question.  Why is soft_reset preferred to sleep mode?

Not a silly question. I actually debated this when initially implementing the
driver. The datasheet describes soft-reset behavior in section 4.9, the
following snippet from the datasheet is particularly relevant:

> The softreset performs a fundamental reset to the device which is largely
> equivalent to a power cycle. Following a delay, all user configuration
> settings are overwritten with their default state...

Sleep mode is the default power-mode, so the only real difference would be that
the oversampling ratio, sampling frequency, and scale would all be reset to
their defaults with a soft-reset. If we just set the power-mode to sleep mode,
the user configuration registers would be preserved.

I can add a comment about the behavior of a softreset in bma400_remove.

Cheers,

 - Dan

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