Re: [PATCH v3] iio: adc: stm32: add oversampling support

[Andy Shevchenko <andy@kernel.org>]

On Tue, Apr 08, 2025 at 07:30:53PM +0200, Olivier Moysan wrote:
> Add oversampling support for STM32H7, STM32MP15 & STM32MP13.
> STM32F4 ADC has no oversampling feature.
> 
> The current support of the oversampling feature aims at increasing
> the data SNR, without changing the data resolution.
> As the oversampling by itself increases data resolution,
> a right shift is applied to keep initial resolution.
> Only the oversampling ratio corresponding to a power of two are
> supported here, to get a direct link between right shift and
> oversampling ratio. (2exp(n) ratio <=> n right shift)
> 
> The oversampling ratio is shared by all channels, whatever channel type.
> (e.g. single ended or differential).
> 
> Oversampling can be configured using IIO ABI:
> - oversampling_ratio_available
> - oversampling_ratio

...

> --- a/drivers/iio/adc/stm32-adc-core.h
> +++ b/drivers/iio/adc/stm32-adc-core.h

Does this include bitfield.h and bits.h already?

...

> +static const unsigned int stm32h7_adc_oversampling_avail[] = {
> +	1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024

Leave trailing comma.

> +};
> +
> +static const unsigned int stm32mp13_adc_oversampling_avail[] = {
> +	1, 2, 4, 8, 16, 32, 64, 128, 256

As well.

>  };

...

> +	.oversampling = stm32h7_adc_oversampling_avail,
>  	.num_res = ARRAY_SIZE(stm32h7_adc_resolutions),
> +	.num_ovs = ARRAY_SIZE(stm32h7_adc_oversampling_avail),

+ array_size.h

...

> +static void stm32h7_adc_set_ovs(struct iio_dev *indio_dev, u32 ovs_idx)
> +{
> +	struct stm32_adc *adc = iio_priv(indio_dev);
> +	u32 ovsr_bits, bits, msk;
> +
> +	msk = STM32H7_ROVSE | STM32H7_OVSR_MASK | STM32H7_OVSS_MASK;
> +	stm32_adc_clr_bits(adc, STM32H7_ADC_CFGR2, msk);
> +
> +	if (!ovs_idx)
> +		return;
> +
> +	/*
> +	 * Only the oversampling ratios corresponding to 2*exp(ovs_idx) are exposed in sysfs.
> +	 * Oversampling ratios [2,3,...,1024] are mapped on OVSR register values [1,2,...,1023].
> +	 * OVSR = 2 exp(ovs_idx) - 1
> +	 * These ratio increase the resolution by ovs_idx bits. Apply a right shift to keep initial
> +	 * resolution given by "assigned-resolution-bits" property.
> +	 * OVSS = ovs_idx
> +	 */
> +	ovsr_bits = (1 << ovs_idx) - 1;

Why not GENMASK(ovs_idx - 1, 0)?

> +	bits = STM32H7_ROVSE | STM32H7_OVSS(ovs_idx) | STM32H7_OVSR(ovsr_bits);
> +
> +	stm32_adc_set_bits(adc, STM32H7_ADC_CFGR2, bits & msk);
> +}
> +
> +static void stm32mp13_adc_set_ovs(struct iio_dev *indio_dev, u32 ovs_idx)
> +{
> +	struct stm32_adc *adc = iio_priv(indio_dev);
> +	u32 bits, msk;
> +
> +	msk = STM32H7_ROVSE | STM32MP13_OVSR_MASK | STM32MP13_OVSS_MASK;
> +	stm32_adc_clr_bits(adc, STM32H7_ADC_CFGR2, msk);
> +
> +	if (!ovs_idx)
> +		return;
> +
> +	/*
> +	 * The oversampling ratios [2,4,8,..,256] are mapped on OVSR register values [0,1,...,7].
> +	 * OVSR = ovs_idx - 1
> +	 * These ratio increase the resolution by ovs_idx bits. Apply a right shift to keep initial
> +	 * resolution given by "assigned-resolution-bits" property.
> +	 * OVSS = ovs_idx
> +	 */
> +	bits = STM32H7_ROVSE | STM32MP13_OVSS(ovs_idx);
> +	if (ovs_idx - 1)
> +		bits |= STM32MP13_OVSR(ovs_idx - 1);
> +
> +	stm32_adc_set_bits(adc, STM32H7_ADC_CFGR2, bits & msk);
> +}

...

> +static int stm32_adc_write_raw(struct iio_dev *indio_dev,
> +			       struct iio_chan_spec const *chan,
> +			       int val, int val2, long mask)
> +{
> +	struct stm32_adc *adc = iio_priv(indio_dev);
> +	struct device *dev = indio_dev->dev.parent;
> +	int nb = adc->cfg->adc_info->num_ovs;
> +	u32 idx;

Why this strange type for loop iterator? Shouldn't be as simple as unsigned int?

> +	int ret;
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
> +		if (val2)
> +			return -EINVAL;
> +
> +		for (idx = 0; idx < nb; idx++)
> +			if (adc->cfg->adc_info->oversampling[idx] == val)
> +				break;

> +

Unneeded blank line as this two are coupled well together.

> +		if (idx >= nb)
> +			return -EINVAL;
> +
> +		if (!iio_device_claim_direct(indio_dev))
> +			return -EBUSY;
> +
> +		ret = pm_runtime_resume_and_get(dev);
> +		if (ret < 0)
> +			goto err;
> +
> +		adc->cfg->set_ovs(indio_dev, idx);
> +
> +		pm_runtime_mark_last_busy(dev);
> +		pm_runtime_put_autosuspend(dev);
> +
> +		adc->ovs_idx = idx;

> +err:



> +		iio_device_release_direct(indio_dev);
> +
> +		return ret;
> +	default:
> +		return -EINVAL;
> +	}
> +}

-- 
With Best Regards,
Andy Shevchenko