Commit 9f57110d authored by Fabrice Gasnier's avatar Fabrice Gasnier Committed by Jonathan Cameron
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iio: adc: stm32-dfsdm: improve sampling frequency accuracy 



The sample frequency is driven using the oversampling ratio depending
on the SPI bus frequency.
Currently, oversampling ratio is computed by an entire division:
- spi_freq / sample_freq. This may result in inaccurate value.
Using DIV_ROUND_CLOSEST improves resulting sample frequency, which is
useful for audio that requests fixed rates (such as: 8, 16 or 32 kHz).
BTW, introduce new routine to re-factor sample frequency setting, and
move frequency accuracy message from warning to debug level.

Signed-off-by: default avatarFabrice Gasnier <fabrice.gasnier@st.com>
Signed-off-by: default avatarJonathan Cameron <Jonathan.Cameron@huawei.com>
parent 65500c53

drivers/iio/adc/stm32-dfsdm-adc.c

+30 −26
Original line number Diff line number Diff line
@@ -558,13 +558,38 @@ static ssize_t dfsdm_adc_audio_get_spiclk(struct iio_dev *indio_dev, 
	return snprintf(buf, PAGE_SIZE, "%d\n", adc->spi_freq);

}



static int dfsdm_adc_set_samp_freq(struct iio_dev *indio_dev,

				   unsigned int sample_freq,

				   unsigned int spi_freq)

{

	struct stm32_dfsdm_adc *adc = iio_priv(indio_dev);

	struct stm32_dfsdm_filter *fl = &adc->dfsdm->fl_list[adc->fl_id];

	unsigned int oversamp;

	int ret;



	oversamp = DIV_ROUND_CLOSEST(spi_freq, sample_freq);

	if (spi_freq % sample_freq)

		dev_dbg(&indio_dev->dev,

			"Rate not accurate. requested (%u), actual (%u)\n",

			sample_freq, spi_freq / oversamp);



	ret = stm32_dfsdm_set_osrs(fl, 0, oversamp);

	if (ret < 0) {

		dev_err(&indio_dev->dev, "No filter parameters that match!\n");

		return ret;

	}

	adc->sample_freq = spi_freq / oversamp;

	adc->oversamp = oversamp;



	return 0;

}



static ssize_t dfsdm_adc_audio_set_spiclk(struct iio_dev *indio_dev,

					  uintptr_t priv,

					  const struct iio_chan_spec *chan,

					  const char *buf, size_t len)

{

	struct stm32_dfsdm_adc *adc = iio_priv(indio_dev);

	struct stm32_dfsdm_filter *fl = &adc->dfsdm->fl_list[adc->fl_id];

	struct stm32_dfsdm_channel *ch = &adc->dfsdm->ch_list[chan->channel];

	unsigned int sample_freq = adc->sample_freq;

	unsigned int spi_freq;
@@ -583,18 +608,10 @@ static ssize_t dfsdm_adc_audio_set_spiclk(struct iio_dev *indio_dev, 
		return -EINVAL;



	if (sample_freq) {

		if (spi_freq % sample_freq)

			dev_warn(&indio_dev->dev,

				 "Sampling rate not accurate (%d)\n",

				 spi_freq / (spi_freq / sample_freq));



		ret = stm32_dfsdm_set_osrs(fl, 0, (spi_freq / sample_freq));

		if (ret < 0) {

			dev_err(&indio_dev->dev,

				"No filter parameters that match!\n");

		ret = dfsdm_adc_set_samp_freq(indio_dev, sample_freq, spi_freq);

		if (ret < 0)

			return ret;

	}

	}

	adc->spi_freq = spi_freq;



	return len;
@@ -1068,23 +1085,10 @@ static int stm32_dfsdm_write_raw(struct iio_dev *indio_dev, 
			spi_freq = adc->spi_freq;

		}



		if (spi_freq % val)

			dev_warn(&indio_dev->dev,

				 "Sampling rate not accurate (%d)\n",

				 spi_freq / (spi_freq / val));



		ret = stm32_dfsdm_set_osrs(fl, 0, (spi_freq / val));

		if (ret < 0) {

			dev_err(&indio_dev->dev,

				"Not able to find parameter that match!\n");

		ret = dfsdm_adc_set_samp_freq(indio_dev, val, spi_freq);

		iio_device_release_direct_mode(indio_dev);

		return ret;

	}

		adc->sample_freq = val;

		iio_device_release_direct_mode(indio_dev);



		return 0;

	}



	return -EINVAL;

}

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