linux-kernel - Re: [PATCH v3 6/6] iio: pressure: Add triggered buffer support for BMP280 driver

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Message-ID: <20240320174602.GA36450@vamoiridPC>
Date: Wed, 20 Mar 2024 18:46:02 +0100
From: Vasileios Amoiridis <vassilisamir@...il.com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Vasileios Amoiridis <vassilisamir@...il.com>, jic23@...nel.org,
	lars@...afoo.de, ang.iglesiasg@...il.com, mazziesaccount@...il.com,
	ak@...klinger.de, petre.rodan@...dimension.ro, phil@...pberrypi.com,
	579lpy@...il.com, linus.walleij@...aro.org,
	semen.protsenko@...aro.org, linux-iio@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 6/6] iio: pressure: Add triggered buffer support for
 BMP280 driver

On Wed, Mar 20, 2024 at 01:16:03PM +0200, Andy Shevchenko wrote:
> On Tue, Mar 19, 2024 at 01:29:25AM +0100, Vasileios Amoiridis wrote:
> > BMP2xx, BMP3xx, and BMP5xx use consecutive buffers for their
> > temperature, pressure and humidity readings. This facilitates
> > the use of burst reads in order to acquire data much faster
> > and in a different way from the one used in oneshot captures.
> > 
> > BMP085 and BMP180 use a completely different measurement
> > process that is well defined and is used in their buffer_handler().
> 
> ...
> 
> >  	ret = regmap_bulk_read(data->regmap, BMP280_REG_TEMP_MSB,
> > -			       data->buf, sizeof(data->buf));
> > +			       data->buf, BMP280_NUM_TEMP_BYTES);
> 
> >  	ret = regmap_bulk_read(data->regmap, BMP280_REG_PRESS_MSB,
> > -			       data->buf, sizeof(data->buf));
> > +			       data->buf, BMP280_NUM_PRESS_BYTES);
> 
> >  	ret = regmap_bulk_read(data->regmap, BMP280_REG_HUMIDITY_MSB,
> > -			       &data->be16, sizeof(data->be16));
> > +			       &data->be16, BME280_NUM_HUMIDITY_BYTES);
> 
> > -	adc_humidity = be16_to_cpu(data->be16);
> > +	adc_humidity = get_unaligned_be16(&data->be16);
> 
> >  	ret = regmap_bulk_read(data->regmap, BMP380_REG_TEMP_XLSB,
> > -			       data->buf, sizeof(data->buf));
> > +			       data->buf, BMP280_NUM_TEMP_BYTES);
> 
> >  	ret = regmap_bulk_read(data->regmap, BMP380_REG_PRESS_XLSB,
> > -			       data->buf, sizeof(data->buf));
> > +			       data->buf, BMP280_NUM_PRESS_BYTES);
> 
> >  	ret = regmap_bulk_read(data->regmap, BMP580_REG_TEMP_XLSB, data->buf,
> > -			       sizeof(data->buf));
> > +			       BMP280_NUM_TEMP_BYTES);
> 
> >  	ret = regmap_bulk_read(data->regmap, BMP580_REG_PRESS_XLSB, data->buf,
> > -			       sizeof(data->buf));
> > +			       BMP280_NUM_PRESS_BYTES);
> 
> These smell to me as candidates to a separate patch with more explanation why.
> (Yes, with the definitions you introduced.) But I leave it to Jonathan to
> decide if we need to split.
> 
> ...
> 
> The below are applicable to the bmp280_buffer_handler(),
> bmp380_buffer_handler() implementations as well.
> 
> ...
> 
> > +	/* Burst read data registers */
> > +	ret = regmap_bulk_read(data->regmap, BMP580_REG_TEMP_XLSB,
> > +			       data->buf, 6);
> 
> Magic size.
> 

Hi Andy,

Thank you again for your feedback. When I was writing it, it was 
looking as a magic number to me as well but then I though that 
since I put the comment above it could be obvious. Now that I see 
it again, I think it was not a good idea and maybe some type of 
definition like

	#define BMP280_BURST_READ_NUM_BYTES 6
	#define BME280_BURST_READ_NUM_BYTES 8

could look better and be more intuitive.

> ...
> 
> > +	/* Temperature calculations */
> > +	memcpy(&chan_value, &data->buf[3], 3);
> 
> _le24() + sign_extend32()?
> 

In the next line from your comment the _le24 or _be24 takes place.
If the sign_extend32() is needed here, shouldn't it also be used
in all the oneshot captures as well?

> ...
> 
> > +	/* Pressure calculations */
> > +	memcpy(&chan_value, &data->buf[0], 3);
> 
> _le24() + sign_extend32()?
> 
> ...
> 
> >  	/*
> > -	 * Maximum number of consecutive bytes read for a temperature or
> > -	 * pressure measurement is 3.
> > +	 * Maximum number of a burst read for temperature, pressure, humidity
> > +	 * is 8 bytes.
> >  	 */
> > -	if (val_size > 3)
> > +	if (val_size > 8)
> 
> sizeof() / new definition for the buf[] size?
> 

In a previous commit that I was fixing this SPI driver, Jonathan had mentioned
that there is no need for a specific definition since it will only be used
here so that's why I kept it as is.

Cheers,
Vasilis
> >  		return -EINVAL;
> 
> -- 
> With Best Regards,
> Andy Shevchenko
> 
>