linux-kernel - Re: [PATCH v5 6/7] iio: add MEMSensing MSA311 3-axis accelerometer driver

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Date:   Fri, 12 Aug 2022 17:10:38 +0000
From:   Dmitry Rokosov <DDRokosov@...rdevices.ru>
To:     "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "jic23@...nel.org" <jic23@...nel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "andriy.shevchenko@...ux.intel.com" 
        <andriy.shevchenko@...ux.intel.com>,
        "andy.shevchenko@...il.com" <andy.shevchenko@...il.com>,
        "christophe.jaillet@...adoo.fr" <christophe.jaillet@...adoo.fr>,
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        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "stephan@...hold.net" <stephan@...hold.net>,
        "daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
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CC:     "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
        kernel <kernel@...rdevices.ru>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 6/7] iio: add MEMSensing MSA311 3-axis accelerometer
 driver

Hello Jonathan and Andy,

Please find a few comments below. They explain why I didn't do something
which was mentioned or suggested in the v4.

On Fri, Aug 12, 2022 at 04:52:29PM +0000, Dmitry Rokosov wrote:

[...]

> +/*
> + * Possible Full Scale ranges
> + *
> + * Axis data is 12-bit signed value, so
> + *
> + * fs0 = (2 + 2) * 9.81 / (2^11) = 0.009580
> + * fs1 = (4 + 4) * 9.81 / (2^11) = 0.019160
> + * fs2 = (8 + 8) * 9.81 / (2^11) = 0.038320
> + * fs3 = (16 + 16) * 9.81 / (2^11) = 0.076641
> + */
> +enum {
> +	MSA311_FS_2G,
> +	MSA311_FS_4G,
> +	MSA311_FS_8G,
> +	MSA311_FS_16G,
> +};
> +
> +static const struct {
> +	int val;
> +	int val2;
> +} msa311_fs_table[] = {
> +	{0, 9580}, {0, 19160}, {0, 38320}, {0, 76641}
> +};
> +
> +/* Possible Output Data Rate values */
> +enum {
> +	MSA311_ODR_1_HZ,
> +	MSA311_ODR_1_95_HZ,
> +	MSA311_ODR_3_9_HZ,
> +	MSA311_ODR_7_81_HZ,
> +	MSA311_ODR_15_63_HZ,
> +	MSA311_ODR_31_25_HZ,
> +	MSA311_ODR_62_5_HZ,
> +	MSA311_ODR_125_HZ,
> +	MSA311_ODR_250_HZ,
> +	MSA311_ODR_500_HZ,
> +	MSA311_ODR_1000_HZ,
> +};
> +
> +static const struct {
> +	int val;
> +	int val2;
> +} msa311_odr_table[] = {
> +	{1, 0}, {1, 950000}, {3, 900000}, {7, 810000}, {15, 630000},
> +	{31, 250000}, {62, 500000}, {125, 0}, {250, 0}, {500, 0}, {1000, 0}
> +};

I didn't change odr and fs table structures to s32_fract, because they
don't have numerator/denominator format, but it's an integer.fractional
format. I didn't find such a common struct for this format. If we want to
generalize such a fractional number format, I suppose it's better to do it
in the separate patch series over the whole IIO subsystem, due to the many
val.val2-like structures inside it.

[...]

> +/**
> + * struct msa311_priv - MSA311 internal private state
> + * @regs: Underlying I2C bus adapter used to abstract slave
> + *        register accesses
> + * @fields: Abstract objects for each registers fields access
> + * @dev: Device handler associated with appropriate bus client
> + * @lock: Protects msa311 device state between setup and data access routines
> + *        (power transitions, samp_freq/scale tune, retrieving axes data, etc)
> + * @chip_name: Chip name in the format "msa311-%hhx" % partid
> + * @new_data_trig: Optional NEW_DATA interrupt driven trigger used
> + *                 to notify external consumers a new sample is ready
> + * @vdd: Optional external voltage regulator for the device power supply
> + */
> +struct msa311_priv {
> +	struct regmap *regs;
> +	struct regmap_field *fields[F_MAX_FIELDS];
> +
> +	struct device *dev;

I stay struct device *dev pointer in the msa311 private structure,
because without it code looks more grubby and we can't retrieve indio_dev
from msa311_priv object using container_of or something else
(it's just a dynamic pointer).

> +	struct mutex lock;

I've removed the state guard comment, but checkpatch.pl is still raising
a warning.

[...]

> +	err = msa311_chip_init(msa311);
> +	if (err)
> +		return err;
> +
> +	indio_dev->modes = INDIO_DIRECT_MODE;

I returned INDIO_DIRECT_MODE initialization, but actually I'm not sure
if it's needed when we setup buffer mode regardless of any optional
parameters.

[...]

-- 
Thank you,
Dmitry