Re: [PATCH 2/3] iio: adc: add stm32 mdf support

[Jonathan Cameron <jic23@kernel.org>]

On Thu, 1 Oct 2026 16:56:46 +0200
Olivier Moysan <olivier.moysan@foss.st.com> wrote:

> Add the STM32 Multi-function Digital Filter (MDF) core, serial interface
> and digital filter drivers. The MDF converts bitstreams from sigma-delta
> modulators or digital microphones into samples exposed through IIO.
> 
> Audio: capture PDM microphones via cyclic DMA for an ASoC consumer.
> Support CIC scaling and filtering, synchronized and interleaving modes.
> Audio use case requires a DMIC filter, and a separate ASoC DAI.
> 
> Analog: expose sigma-delta modulators as IIO voltage channels with
> direct reads or DMA buffering mode. STM32 timer triggers can be used as
> clock source.
> Analog use case requires an IIO backend for the SD modulator.
> 
> Signed-off-by: Olivier Moysan <olivier.moysan@foss.st.com>

I'm not going to spend long on this today, but a few trivial things noted
from a quick glance.

> diff --git a/drivers/iio/adc/stm32-mdf-serial.c b/drivers/iio/adc/stm32-mdf-serial.c
> new file mode 100644
> index 000000000000..15a58cf833be
> --- /dev/null
> +++ b/drivers/iio/adc/stm32-mdf-serial.c

...

> +
> +int stm32_mdf_sitf_stop(struct stm32_mdf_sitf *sitf)
> +{
> +	int ret = 0;
> +
> +	spin_lock(&sitf->lock);

Use guard() for cases like this. Simplifies the flow and helps
readabilty as a result.  Everyone loves an early return.

> +
> +	if (!sitf->refcnt) {
> +		dev_err(sitf->dev, "Unbalanced serial interface stop ?\n");
> +		ret = -EPERM;
> +		goto out;
> +	} else {
> +		sitf->refcnt--;
> +	}
> +
> +	if (!sitf->refcnt)
> +		ret = regmap_clear_bits(sitf->regmap, MDF_SITFCR_REG, MDF_SITFCR_SITFEN);
> +
> +out:
> +	spin_unlock(&sitf->lock);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(stm32_mdf_sitf_stop);
>
> +static int stm32_mdf_sitf_runtime_suspend(struct device *dev)
> +{
Add a comment on why you need these.
> +	return 0;
> +}
> +
> +static int stm32_mdf_sitf_runtime_resume(struct device *dev)
> +{
> +	return 0;
> +}

> diff --git a/drivers/iio/adc/stm32-mdf.h b/drivers/iio/adc/stm32-mdf.h
> new file mode 100644
> index 000000000000..7e403c26d4dc
> --- /dev/null
> +++ b/drivers/iio/adc/stm32-mdf.h
> @@ -0,0 +1,312 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +/*
> + * This file is part of STM32 MDF driver
> + *
> + * Copyright (C) 2023, STMicroelectronics - All Rights Reserved
I'd guess you'll modify it enough that this might need
an update!


> +/* MDF_SIDR: Size Identification Register */
> +#define MDF_SIDR_SID_MASK GENMASK(31, 0)
> +#define MDF_SIDR_SID(v) FIELD_PREP(MDF_SIDR_SID_MASK, v)
I'd not bother with the second macro.  It is only a little
shorter than FIELD_PREP() in most case.

>