Re: [PATCH v3 11/11] iio: dac: add mcf54415 DAC

On Fri, 22 May 2026 23:20:39 +0200
Angelo Dureghello <[email protected]> wrote:

> From: Angelo Dureghello <[email protected]>
> 
> Add basic version of mcf54415 DAC driver. DAC is embedded in the cpu and
> 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.
> 
> Signed-off-by: Angelo Dureghello <[email protected]>
https://sashiko.dev/#/patchset/20260522-wip-stmark2-dac-v3-0-16be0ad35a67%40baylibre.com

Given there were only a couple of comments I've included them below alongside
my review.  All minor stuff.

Thanks,

Jonathan

> ---
> Changes in v2:
> - remove tests from commit message, moved to patch 0
> - remove additional blank lines
> - remove dead code and unused definitions
> - use regmap
> - add limit check on raw write
> - non functional style fixes
> - add COMPILE_TEST to Kconfig
> Changes in v3:
> - add comments where needed
> - code style changes
> - remove unneeded variables
> - use regmap_set_bits where possible
> - remove macro not needed to define a single channel
> - set up regmap to big_endian accesses for next patches that will come,
>   that will adjust ColdFire readx/writex as standard LE (links in 0/x).
> - add return value check on regmap calls
> - sashiko: remove unneeded .io_port from regmap init.
> - sashiko: add select REGMAP_MMIO in Kconfig

Looks like you missed or disagreed with the previous sashiko comment on v2 about
type passed to regmap_read()

> ---
>  drivers/iio/dac/Kconfig        |  11 +++
>  drivers/iio/dac/Makefile       |   1 +
>  drivers/iio/dac/mcf54415_dac.c | 207 +++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 219 insertions(+)
> 
> diff --git a/drivers/iio/dac/Kconfig b/drivers/iio/dac/Kconfig
> index cd4870b65415..b1a578076188 100644
> --- a/drivers/iio/dac/Kconfig
> +++ b/drivers/iio/dac/Kconfig
> @@ -516,6 +516,17 @@ config MAX5821
>  	  Say yes here to build support for Maxim MAX5821
>  	  10 bits DAC.
>  
> +config MCF54415_DAC
> +	tristate "NXP MCF54415 DAC driver"
> +	depends on M5441x || COMPILE_TEST
> +	select REGMAP_MMIO
> +	help
> +	  Say yes here to build support for NXP MCF54415
> +	  12bit DAC.
> +
> +	  To compile this driver as a module, choose M here: the module
> +	  will be called mcf54415_dac.
> +

> diff --git a/drivers/iio/dac/mcf54415_dac.c b/drivers/iio/dac/mcf54415_dac.c
> new file mode 100644
> index 000000000000..c8c87572d43d
> --- /dev/null
> +++ b/drivers/iio/dac/mcf54415_dac.c
> @@ -0,0 +1,207 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * NXP mcf54415 DAC driver
> + *
> + * Copyright 2026 BayLibre - [email protected]
> + */
> +
> +#include <linux/array_size.h>
> +#include <linux/bitfield.h>
> +#include <linux/bits.h>
> +#include <linux/clk.h>
> +#include <linux/compiler_types.h>
> +#include <linux/delay.h>
> +#include <linux/err.h>
> +#include <linux/io.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>

not seeing any use of this. I guess it 'evolved' away.
Anyhow, please sanity check these all one more time for v4.

> +#include <linux/platform_device.h>
> +#include <linux/regmap.h>
> +
> +#include <linux/iio/iio.h>
> +
> +#define MCF54415_DAC_CR			0x00
> +#define MCF54415_DAC_CR_PDN		BIT(0)
> +#define MCF54415_DAC_CR_HSLS		BIT(6)
> +#define MCF54415_DAC_CR_WMLVL		GENMASK(9, 8)
> +#define MCF54415_DAC_CR_FILT		BIT(12)
> +
> +#define MCF54415_DAC_DATA		0x02
> +
> +struct mcf54415_dac {
> +	struct regmap *map;
> +	struct clk *clk;
> +};
> +
> +static const struct regmap_config mcf54415_dac_regmap_config = {
> +	.reg_bits = 16,
> +	.reg_stride = 2,
> +	.val_bits = 16,
> +	.max_register = 0x0c, /* DACX_FILTCNT,  R.M. Table 30-2 */
> +	.val_format_endian = REGMAP_ENDIAN_BIG,
> +	.reg_format_endian = REGMAP_ENDIAN_BIG,
> +};
> +
> +static int mcf54415_dac_init(struct mcf54415_dac *info)
> +{
> +	int ret;
> +
> +	/* Keeping defaults and enable DAC (bit 0 set to 0) */
> +	ret = regmap_write(info->map, MCF54415_DAC_CR, MCF54415_DAC_CR_FILT |
> +			   FIELD_PREP(MCF54415_DAC_CR_WMLVL, 1));

Perhaps use a local variable. It is a tiny bit too easy to miss that
parameter being split over two lines.

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

would avoid that.

Alternatively perhaps just reflowing as:
	ret = regmap_write(info->map, MCF54415_DAC_CR,
			   MCF54415_DAC_CR_FILT |
			   FIELD_PREP(MCF54415_DAC_CR_WMLVL, 1));

avoids that reading issue (I read it wrong ;)



> +	if (ret)
> +		return ret;
> +
> +	/* DAC is ready after 12us, from RM table 40-3  */
> +	fsleep(12);
> +
> +	return 0;
> +}

> +
> +static int mcf54415_read_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);
> +	int ret;
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_RAW:
> +		ret = regmap_read(info->map, MCF54415_DAC_DATA, val);

Sashiko pointed out that regmap_read() expects a u32* so this should use
a local variable for the read.

> +		if (ret)
> +			return -EIO;

Another one sashiko got. Why is this eating the possibly more useful error
code from regmap_read()?

> +		*val &= 0xfff;
> +		return IIO_VAL_INT;
> +	case IIO_CHAN_INFO_SCALE:
> +		/* Reference voltage as per ColdFire datasheet is 3.3V */
> +		*val = 3300 /* mV */;
> +		*val2 = 12;
> +		return IIO_VAL_FRACTIONAL_LOG2;
> +	default:
> +		return -EINVAL;
> +	}
> +}

> +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;
> +
> +	mcf54415_dac_init(info);
If this fails should we report it?  I think you'd at least want
some print to help with debug. (Sashiko got this)

> +
> +	return 0;
> +}