Re: [PATCH v2 3/7] iio: adc: add RZ/T2H / RZ/N2H ADC driver

[Jonathan Cameron <jic23@kernel.org>]

On Fri, 26 Sep 2025 01:40:05 +0300
Cosmin Tanislav <cosmin-gabriel.tanislav.xa@renesas.com> wrote:

> Add support for the A/D 12-Bit successive approximation converters found
> in the Renesas RZ/T2H (R9A09G077) and RZ/N2H (R9A09G087) SoCs.
> 
> RZ/T2H has two ADCs with 4 channels and one with 6.
> RZ/N2H has two ADCs with 4 channels and one with 15.
> 
> Conversions can be performed in single or continuous mode. Result of the
> conversion is stored in a 16-bit data register corresponding to each
> channel.
> 
> The conversions can be started by a software trigger, a synchronous
> trigger (from MTU or from ELC) or an asynchronous external trigger (from
> ADTRGn# pin).
> 
> Only single mode with software trigger is supported for now.
> 
> Signed-off-by: Cosmin Tanislav <cosmin-gabriel.tanislav.xa@renesas.com>

Hi Cosmin

A few minor comments inline.  Nice little driver.

Jonathan

> diff --git a/drivers/iio/adc/rzt2h_adc.c b/drivers/iio/adc/rzt2h_adc.c
> new file mode 100644
> index 000000000000..6a49788a5c67
> --- /dev/null
> +++ b/drivers/iio/adc/rzt2h_adc.c
> @@ -0,0 +1,306 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/bitfield.h>
> +#include <linux/cleanup.h>
> +#include <linux/completion.h>
> +#include <linux/delay.h>
> +#include <linux/iio/adc-helpers.h>
> +#include <linux/iio/iio.h>
> +#include <linux/interrupt.h>
> +#include <linux/io.h>
> +#include <linux/iopoll.h>
> +#include <linux/mod_devicetable.h>
> +#include <linux/module.h>
> +#include <linux/platform_device.h>
> +#include <linux/pm_runtime.h>
> +#include <linux/property.h>
> +
> +#define RZT2H_NAME			"rzt2h-adc"

> +
> +static void rzt2h_adc_start_stop(struct rzt2h_adc *adc, bool start,
> +				 unsigned int conversion_type)
> +{
> +	u16 mask;
> +	u16 reg;

Might as well use one line for those.

> +
> +	reg = readw(adc->base + RZT2H_ADCSR_REG);
> +
> +	if (start) {

To me having a shared function for start and stop isn't adding much here. I'd
just spit it and avoid the conditionals and passing a conversion type into stop
which makes no sense.

> +		/* Set conversion type */
> +		reg &= ~RZT2H_ADCSR_ADCS_MASK;
> +		reg |= FIELD_PREP(RZT2H_ADCSR_ADCS_MASK, conversion_type);
FIELD_MODIFY()

> +	}
> +
> +	/* Toggle end of conversion interrupt and start bit. */
> +	mask = RZT2H_ADCSR_ADIE_MASK | RZT2H_ADCSR_ADST_MASK;
> +	if (start)
> +		reg |= mask;
> +	else
> +		reg &= ~mask;
> +
> +	writew(reg, adc->base + RZT2H_ADCSR_REG);
> +}
> +
> +static int rzt2h_adc_read_single(struct rzt2h_adc *adc, unsigned int ch, int *val)
> +{
> +	int ret;
> +
> +	ret = pm_runtime_resume_and_get(adc->dev);
> +	if (ret)
> +		return ret;
> +
> +	guard(mutex)(&adc->lock);

See other branch of thread and guidance in cleanup.h wrt to gotos.

> +
> +	reinit_completion(&adc->completion);
> +
> +	/* Enable a single channel */
> +	writew(RZT2H_ADANSA0_CH_MASK(ch), adc->base + RZT2H_ADANSA0_REG);
> +
> +	rzt2h_adc_start_stop(adc, true, RZT2H_ADCSR_ADCS_SINGLE);
> +
> +	/*
> +	 * Datasheet Page 2770, Table 41.1:
> +	 * 0.32us per channel when sample-and-hold circuits are not in use.
> +	 */
> +	ret = wait_for_completion_timeout(&adc->completion, usecs_to_jiffies(1));
> +	if (!ret) {
> +		ret = -ETIMEDOUT;
> +		goto disable;
> +	}
> +
> +	*val = readw(adc->base + RZT2H_ADDR_REG(ch));
> +	ret = IIO_VAL_INT;
> +
> +disable:
> +	rzt2h_adc_start_stop(adc, false, 0);
> +
> +	pm_runtime_put_autosuspend(adc->dev);
> +
> +	return ret;
> +}

> +static int rzt2h_adc_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct iio_dev *indio_dev;
> +	struct rzt2h_adc *adc;
> +	int ret;
> +	int irq;

Might as well save a line.

	int ret, irq;

> +
> +	indio_dev = devm_iio_device_alloc(dev, sizeof(*adc));
>