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

[Vasileios Amoiridis]

On Thu, Aug 29, 2024 at 03:31:48PM +0300, Andy Shevchenko wrote:
> 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!
> 

I see your point, I can work this out better.

> > 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

No reason, I can make it unsigned. Unit suffix is a good addition
indeed!!!

> 
> 	unsigned int meas_time_us;
> 
> (and check the rest of the patch for the similar).
> 

True, thanks!!!

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

ACK.

> > +	/* 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.
> 

It seems I have indentation issues in other places as well.
I think I remember checkpatch.pl informing me about those but I didn't
got anything back...


> 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).
> 

I see your point, I can try it.

> > +	/* 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?
> 

Well this change is because before, the sensor was by default in
NORMAL_MODE so whenever we were writing a different setting (Output
data rate, oversampling ratio) to the sensor, the NORMAL_MODE was
chosen. There was no idea of SLEEP or FORCED MODE.

While now, since this commits adds the idea of SLEEP_MODE
by default (FORCED_MODE for oneshot captures, and NORMAL_MODE for
buffer/trigger) we need to keep the sensor in SLEEP_MODE as well
when we change its configuration.

I believe it belongs to this commit. Maybe though, I should mention
this change explicitly in the commit message?

> ...
> 
> > +		/*
> > +		 * According to the BMP3 Sensor API, the sensor needs 5000ms
> 
> I believe it's a typo in unit suffix.
> 

Yes indeed its a typo, I wanted to say 5000us. The fsleep(5000) is correct.

> 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?
> 

That could help, yeah!

> > +			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.
> 

ACK.

> 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 */
> 	};
> 

I was not aware of this convention, I can do it.

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

ACK.

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

ACK.

> > +	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?
> 

I can elaborate more in the comment yes.

> > -	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.
> 

I can maybe do it in a separate commit because you have already pointed
out things that could be improved with styling.

> ...
> 
> > +	usleep_range(2500, 3000);
> 
> fsleep()? Comment?
> 

ACK.

> ...
> 
> >  	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?
> 

Yes, that would be good!!!

Cheers,
Vasilis

> -- 
> With Best Regards,
> Andy Shevchenko
> 
>