Subject: Re: [PATCH v4 11/11] iio: dac: add mcf54415 DAC

From: Andy Shevchenko <[email-masked]>
Date: Tue, 2 Jun 2026 12:39:15 +0300

On Sun, May 31, 2026 at 05:26:04PM +0200, Angelo Dureghello wrote:

> Add basic version of mcf54415 DAC driver. DAC is embedded in the cpu and

CPU

(or maybe you wanted use 'SoC' acronym)

> DAC configuration registers are mapped in the internal IO address space.
> 
> The DAC accepts a 12-bit digital signal and creates a monotonic 12-bit
> analog output varying from DAC_VREFL to DAC_VREFH. The DAC module
> consists of a conversion unit, an output amplifier, and the associated
> digital control blocks. Default register values for DAC_VREFL and DAC_VREFH
> are respectively 0 and 0xfff, left untouched in this initial version.
> 
> This initial version of the driver is minimalistic, "output raw" only, to
> be extended in the future. DMA and external sync are disabled, default mode
> is high speed, default format is right-justified 12bit on 16bit word.

Be consistent: 12-bit on 16-bit

...

> Changes in v4:
> - remove unused includes
> - sashiko: return "ret" as regmap_read ret value in case of error

> - sashiko: using u32 as regmap_read value

Why? regmap API uses 'unsigned int'. Then you can take out any bits, fields,
et cetera from it into fixed-width type of variables.

> - use local variable in mcf54415_dac_init() for better readability
> - sashiko: check mcf54415_dac_init return value also in resume()

...

> +#include <linux/bitfield.h>
> +#include <linux/bits.h>
> +#include <linux/clk.h>

> +#include <linux/compiler_types.h>

Drop this (see below).

> +#include <linux/delay.h>
> +#include <linux/err.h>
> +#include <linux/io.h>
> +#include <linux/module.h>
> +#include <linux/platform_device.h>
> +#include <linux/regmap.h>

+ types.h (it also guarantees compile_types.h).

...

> +static int mcf54415_dac_init(struct mcf54415_dac *info)
> +{
> +	int ret;
> +	u16 val = MCF54415_DAC_CR_FILT | FIELD_PREP(MCF54415_DAC_CR_WMLVL, 1);

Can we move towards reversed xmas tree order?

	u16 val = MCF54415_DAC_CR_FILT | FIELD_PREP(MCF54415_DAC_CR_WMLVL, 1);
	int ret;

> +	/* Fixed defaults and enable DAC (bit 0 set to 0) */
> +	ret = regmap_write(info->map, MCF54415_DAC_CR, val);
> +	if (ret)
> +		return ret;
> +
> +	/* DAC is ready after 12us, from RM table 40-3  */
> +	fsleep(12);
> +
> +	return 0;
> +}

...

> +static int mcf54415_write_raw(struct iio_dev *indio_dev,
> +			      struct iio_chan_spec const *chan,
> +			      int val, int val2, long mask)
> +{
> +	struct mcf54415_dac *info = iio_priv(indio_dev);
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_RAW:
> +		/* Check based on RM 30.3.2 (DACn_DATA) reg. resolution */
> +		if (val < 0 || val > 4095)
> +			return -EINVAL;
> +		return regmap_write(info->map, MCF54415_DAC_DATA, val);

So, for example, -1 will be written as 0xffffffff (with the respective bits
taken into account). Is it a problem?

> +	default:
> +		return -EINVAL;
> +	}
> +}

...

> +static int mcf54415_dac_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct iio_dev *indio_dev;
> +	struct mcf54415_dac *info;
> +	void __iomem *regs;
> +	int ret;
> +
> +	indio_dev = devm_iio_device_alloc(dev, sizeof(*info));
> +	if (!indio_dev)
> +		return -ENOMEM;
> +
> +	info = iio_priv(indio_dev);
> +
> +	regs = devm_platform_ioremap_resource(pdev, 0);
> +	if (IS_ERR(regs))
> +		return dev_err_probe(dev, PTR_ERR(regs),
> +				     "failed to get io regs\n");

One line. It's more than decade that checkpatch stopped complaining on
the trailing string literals.

> +	info->map = devm_regmap_init_mmio(dev, regs,
> +					  &mcf54415_dac_regmap_config);

One line (yes, 82 characters).

> +	if (IS_ERR(info->map))
> +		return PTR_ERR(info->map);
> +
> +	info->clk = devm_clk_get_enabled(dev, "dac");
> +	if (IS_ERR(info->clk))
> +		return dev_err_probe(dev, PTR_ERR(info->clk),
> +				     "failed getting clock\n");

Also one line.

> +	platform_set_drvdata(pdev, indio_dev);
> +
> +	indio_dev->name = "mcf54415";
> +	indio_dev->info = &mcf54415_dac_iio_info;
> +	indio_dev->modes = INDIO_DIRECT_MODE;
> +	indio_dev->channels = &mcf54415_dac_iio_channel;
> +	indio_dev->num_channels = 1;
> +
> +	ret = mcf54415_dac_init(info);
> +	if (ret)
> +		return ret;
> +
> +	ret = devm_add_action_or_reset(dev, mcf54415_dac_exit, info);
> +	if (ret)
> +		return ret;
> +
> +	return devm_iio_device_register(dev, indio_dev);
> +}

...

> +static int mcf54415_dac_resume(struct device *dev)
> +{
> +	struct mcf54415_dac *info = iio_priv(dev_get_drvdata(dev));
> +	int ret;
> +
> +	ret = clk_prepare_enable(info->clk);
> +	if (ret)
> +		return ret;
> +
> +	ret = mcf54415_dac_init(info);
> +	if (ret) {
> +		dev_err(dev, "could not resume device\n");
> +		return ret;
> +	}
> +
> +	return 0;

> +

Besides stray blank line the above can be

	ret = mcf54415_dac_init(info);
	if (ret)
		dev_err(dev, "could not resume device\n");

	return ret;

> +}

-- 
With Best Regards,
Andy Shevchenko