linux-kernel - Re: [PATCH v2 2/2] iio: dac: Add MAX22007 DAC driver support

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Message-ID: <20260111160914.72f177e6@jic23-huawei>
Date: Sun, 11 Jan 2026 16:09:14 +0000
From: Jonathan Cameron <jic23@...nel.org>
To: Janani Sunil <janani.sunil@...log.com>
Cc: Lars-Peter Clausen <lars@...afoo.de>, Michael Hennerich
 <Michael.Hennerich@...log.com>, Alexandru Ardelean
 <alexandru.ardelean@...log.com>, "Rob Herring" <robh@...nel.org>, Krzysztof
 Kozlowski <krzk+dt@...nel.org>, "Conor Dooley" <conor+dt@...nel.org>,
 Jonathan Corbet <corbet@....net>, <linux-iio@...r.kernel.org>,
 <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
 <linux-doc@...r.kernel.org>, <jan.sun97@...il.com>
Subject: Re: [PATCH v2 2/2] iio: dac: Add MAX22007 DAC driver support

On Thu, 8 Jan 2026 13:58:24 +0100
Janani Sunil <janani.sunil@...log.com> wrote:

> Add support for the MAX22007, a 4-channel 12-bit DAC that drives
> voltage or current output on each channel.
> 
> Signed-off-by: Janani Sunil <janani.sunil@...log.com>

A few minor things to add to Marcelo's detailed review.

Thanks,

Jonathan

> diff --git a/drivers/iio/dac/max22007.c b/drivers/iio/dac/max22007.c
> new file mode 100644
> index 000000000000..19557c008554
> --- /dev/null
> +++ b/drivers/iio/dac/max22007.c


> +static int max22007_spi_read(void *context, const void *reg, size_t reg_size,
> +			     void *val, size_t val_size)
> +{
> +	struct max22007_state *st = context;
> +	u8 reg_byte = *(u8 *)reg;
> +	u8 calculated_crc, received_crc;
> +	u8 crc_data[3];
> +	u8 rx_buf[4];
> +	int ret;
> +
> +	if (reg_size != 1)
> +		return -EINVAL;
> +
> +	ret = spi_write_then_read(st->spi, &reg_byte, 1, rx_buf,
> +				  val_size + MAX22007_CRC_OVERHEAD);
> +	if (ret) {
> +		dev_err(&st->spi->dev, "SPI transfer failed: %d\n", ret);
> +		return ret;
> +	}
> +
> +	crc_data[0] = reg_byte;
> +	crc_data[1] = rx_buf[0];
> +	crc_data[2] = rx_buf[1];
> +
> +	calculated_crc = crc8(max22007_crc8_table, crc_data, 3, 0x00);

I think you can chain CRCs as follows and avoid the need for a local array
just to marshal the data.

	calculated_crc = crc8(max22007_crc8_table, &reg_byte, 1, 0x00);
	calculated_crc = crc8(max22007_crc8_table, rx_buf, 2, caculated_crc);

> +	received_crc = rx_buf[val_size];
> +
> +	if (calculated_crc != received_crc) {
> +		dev_err(&st->spi->dev, "CRC mismatch on read register %02x\n", reg_byte);
> +		return -EIO;
> +	}
> +
> +	memcpy(val, rx_buf, val_size);
> +
> +	return 0;
> +}

> +static ssize_t max22007_write_dac_powerdown(struct iio_dev *indio_dev,
> +					    uintptr_t private,
> +					    const struct iio_chan_spec *chan,
> +					    const char *buf, size_t len)
> +{
> +	struct max22007_state *st = iio_priv(indio_dev);
> +	bool powerdown;
> +	int ret;
> +
> +	ret = kstrtobool(buf, &powerdown);
> +	if (ret)
> +		return ret;
> +
> +	if (powerdown)
> +		ret = regmap_update_bits(st->regmap, MAX22007_CHANNEL_MODE_REG,
> +					 MAX22007_CH_PWRON_CH_MASK(chan->channel),
> +					 MAX22007_CH_PWR_VAL(chan->channel, 0));
> +	else
> +		ret = regmap_update_bits(st->regmap, MAX22007_CHANNEL_MODE_REG,
> +					 MAX22007_CH_PWRON_CH_MASK(chan->channel),
> +					 MAX22007_CH_PWR_VAL(chan->channel, 1));
> +	if (ret)
> +		return ret;
> +
Something like the following reduces duplication:

	ret = regmap_update_bits(st->regmap, MAX22007_CHANNEL_MODE_REG,
				 MAX2207_CH_PWRON_CH_MASK(chan->channel),
				 MAX2207_CH_PWR_VAL(chan->channel, powerdown ? 1 : 0);


> +	return len;
> +}