Re: [PATCH v4 4/7] iio: pressure: bmp280: Use sleep and forced mode for oneshot captures

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Wed, Aug 28, 2024 at 10:51:24PM +0200, Vasileios Amoiridis wrote:
> This commit adds forced mode support in sensors BMP28x, BME28x, BMP3xx

s/This commit, adds/Add/

The imperative mode is documented in Submitting Patches.

> and BMP58x. Sensors BMP18x and BMP085 are old and do not support this
> feature so their operation is not affected at all.
> 
> Essentially, up to now, the rest of the sensors were used in normal mode
> all the time. This means that they are continuously doing measurements
> even though these measurements are not used. Even though the sensor does
> provide PM support, to cover all the possible use cases, the sensor needs
> to go into sleep mode and wake up whenever necessary.
> 
> This commit, adds sleep and forced mode support. Essentially, the sensor

Déjà-vu feeling... Ah, first line is the same!

> sleeps all the time except for when a measurement is requested. When there
> is a request for a measurement, the sensor is put into forced mode, starts
> the measurement and after it is done we read the output and we put it again
> in sleep mode.
> 
> For really fast and more deterministic measurements, the triggered buffer
> interface can be used, since the sensor is still used in normal mode for
> that use case.
> 
> This commit does not add though support for DEEP STANDBY, Low Power NORMAL
> and CONTINUOUS modes, supported only by the BMP58x version.

...

> +static int bmp280_wait_conv(struct bmp280_data *data)
> +{
> +	unsigned int reg;

> +	int ret, meas_time;

Why meas_time is signed?
Also, please name it with a unit suffix

	unsigned int meas_time_us;

(and check the rest of the patch for the similar).

> +
> +

A single blank line is enough. Also check all patches for this.

> +	/* Check if we are using a BME280 device */
> +	if (data->oversampling_humid)

> +		meas_time += BIT(data->oversampling_humid) * BMP280_MEAS_DUR +
> +			       BMP280_PRESS_HUMID_MEAS_OFFSET;

Indentation issue, the same seems in all of similar expressions in this patch.

Also play with this form and check if it looks better

		meas_time += BMP280_PRESS_HUMID_MEAS_OFFSET +
			     BIT(data->oversampling_humid) * BMP280_MEAS_DUR;

(at least I found it better to read as first we apply constants, followed by
 longer variable-based calculations).

> +	/* Pressure measurement time */
> +	meas_time += BIT(data->oversampling_press) * BMP280_MEAS_DUR +
> +		      BMP280_PRESS_HUMID_MEAS_OFFSET;
> +
> +	/* Temperature measurement time */
> +	meas_time += BIT(data->oversampling_temp) * BMP280_MEAS_DUR;
> +
> +	/* Waiting time according to the BM(P/E)2 Sensor API */
> +	fsleep(meas_time);
> +
> +	ret = regmap_read(data->regmap, BMP280_REG_STATUS, &reg);
> +	if (ret) {
> +		dev_err(data->dev, "failed to read status register\n");
> +		return ret;
> +	}
> +
> +	if (reg & BMP280_REG_STATUS_MEAS_BIT) {
> +		dev_err(data->dev, "Measurement cycle didn't complete\n");
> +		return -EBUSY;
> +	}
> +
> +	return 0;
> +}

...

int bmp280_chip_config(struct bmp280_data *data)

>  				BMP280_OSRS_TEMP_MASK |
>  				BMP280_OSRS_PRESS_MASK |
>  				BMP280_MODE_MASK,
> -				osrs | BMP280_MODE_NORMAL);
> +				osrs | BMP280_MODE_SLEEP);
>  	if (ret) {
>  		dev_err(data->dev, "failed to write ctrl_meas register\n");
>  		return ret;

This _feels_ like a separate change. I haven't found anything explicitly
describing it in the commit message. Did I miss it?

...

> +		/*
> +		 * According to the BMP3 Sensor API, the sensor needs 5000ms

I believe it's a typo in unit suffix.

If not, this should be very well described to explain why 5 seconds is needed.

> +		 * in order to go to the sleep mode.
> +		 */
> +		fsleep(5000);

...

> +{
> +	int ret;
> +
> +	switch (mode) {
> +	case BMP280_SLEEP:
> +	case BMP280_NORMAL:
> +		break;
> +	case BMP280_FORCED:
> +		ret = regmap_set_bits(data->regmap, BMP580_REG_DSP_CONFIG,
> +				      BMP580_DSP_IIR_FORCED_FLUSH);
> +		if (ret) {
> +			dev_err(data->dev,
> +				"Could not flush IIR filter constants.\n");

Temporary variable for data->dev?

> +			return ret;
> +		}
> +		break;
> +	default:
> +		return -EINVAL;
> +	}
> +
> +	ret = regmap_write_bits(data->regmap, BMP580_REG_ODR_CONFIG,
> +				BMP580_MODE_MASK,
> +				FIELD_PREP(BMP580_MODE_MASK,
> +					   bmp580_operation_mode[mode]));
> +	if (ret) {
> +		dev_err(data->dev, "failed to  write power control register\n");
> +		return ret;
> +	}
> +
> +	data->op_mode = mode;
> +
> +	return 0;
> +}

...

> +static int bmp580_wait_conv(struct bmp280_data *data)
> +{
> +	/*
> +	 * Taken from datasheet, Section 2 "Specification, Table 3 "Electrical
> +	 * characteristics.
> +	 */
> +	static const int time_conv_press[] = {
> +		0, 1050, 1785, 3045, 5670, 10920, 21420, 42420, 84420
> +	};

Mind the comma at the end.

And in programming hardware we quite often operate with power-of-2 things, so I
recommend to have 8 per line,

	static const int time_conv_press[] = {
		0, 1050, 1785, 3045, 5670, 10920, 21420, 42420,		/* 0-7 */
		84420,							/* 8 */
	};

> +	static const int time_conv_temp[] = {
> +		0, 1050, 1105, 1575, 2205, 3465, 6090, 11340, 21840
> +	};

Ditto.

> +

Stray blank line. This is a definition block, we don't need blank lines in it.

> +	int meas_time;
> +
> +	meas_time = 4 * USEC_PER_MSEC + time_conv_temp[data->oversampling_temp]
> +		      + time_conv_press[data->oversampling_press];
> +
> +	/* Measurement time mentioned in Chapter 2, Table 4 of the datasheet. */
> +	fsleep(meas_time);
> +
> +	return 0;
> +}

...

>  	/* From datasheet's table 4: electrical characteristics */

With this change the comment seems odd. Can you elaborate more?

> -	usleep_range(2500, 3000);
> +	fsleep(data->start_up_time + 500);

Also, can we name it start_up_time_us?
It's fine to postpone renaming if it takes too many unrelated changes.

...

> +	usleep_range(2500, 3000);

fsleep()? Comment?

...

>  	usleep_range(data->start_up_time, data->start_up_time + 100);

This is already in the code, but maybe switching to fsleep() and adding
a comment to explain how it's calculated (based on the spec? Reference?),
so in a separate change?

-- 
With Best Regards,
Andy Shevchenko