Re: [PATCH v4 2/2] iio: add MCP4728 I2C DAC driver

[Jonathan Cameron]

On Thu,  3 Aug 2023 14:56:35 +0200
Andrea Collamati <andrea.collamati@xxxxxxxxx> wrote:

> MCP4728 is a 12-bit quad channel DAC with I2C interface.
> 
> support for:
>  * per-channel gain
>  * per-channel power state
>  * per-channel power down mode control
>  * per-channel vref selection internal/vdd
>  * store current state to on-chip EEPROM
> 
> Signed-off-by: Andrea Collamati <andrea.collamati@xxxxxxxxx>
Hi Andrea,

On this final read through I noticed a few minor things. Rather than
get you to do a v5 I've made the changes whilst applying. Please
take a sanity check at
https://git.kernel.org/pub/scm/linux/kernel/git/jic23/iio.git/log/?h=testing
to make sure I didn't break anything and let me know if I did!

Applied with the below mentioned changes to the togreg branch of iio.git
which is initially pushed out as testing to let 0-day poke at it and see
if it can find any problems.

Thanks,

Jonathan

> diff --git a/drivers/iio/dac/mcp4728.c b/drivers/iio/dac/mcp4728.c
> new file mode 100644
> index 000000000000..ba3eab349b0a
> --- /dev/null
> +++ b/drivers/iio/dac/mcp4728.c
> @@ -0,0 +1,626 @@
...



> +
> +static int mcp4728_set_scale(int channel, struct mcp4728_data *data, int val,
> +			     int val2)
> +{
> +	int scale = mcp4728_find_matching_scale(data, val, val2);
> +
> +	if (scale < 0)
> +		return scale;
> +
> +	switch (scale) {
> +	case MCP4728_SCALE_VDD:
> +		data->chdata[channel].ref_mode = MCP4728_VREF_EXTERNAL_VDD;
> +		break;
> +	case MCP4728_SCALE_VINT_NO_GAIN:
> +		data->chdata[channel].ref_mode = MCP4728_VREF_INTERNAL_2048mV;
> +		data->chdata[channel].g_mode   = MCP4728_GAIN_X1;
> +		break;
> +	case MCP4728_SCALE_VINT_GAIN_X2:
> +		data->chdata[channel].ref_mode = MCP4728_VREF_INTERNAL_2048mV;
> +		data->chdata[channel].g_mode   = MCP4728_GAIN_X2;
> +		break;
> +	default:
> +		return -EINVAL;
> +	}
> +	return 0;

return instead of breaking above as nothing to be done after the switch.
Side effect of that is this return 0 not needed.

> +}

...

> +static int mcp4728_write_raw(struct iio_dev *indio_dev,
> +			     struct iio_chan_spec const *chan, int val,
> +			     int val2, long mask)
> +{
> +	struct mcp4728_data *data = iio_priv(indio_dev);
> +	int ret;
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_RAW:
> +		if (val < 0 || val > GENMASK(MCP4728_RESOLUTION - 1, 0))
> +			return -EINVAL;
> +		data->chdata[chan->channel].dac_value = val;
> +		ret = mcp4728_program_channel_cfg(chan->channel, indio_dev);
> +		break;

Direct returns preferred if no cleanup to do.

> +	case IIO_CHAN_INFO_SCALE:
> +		ret = mcp4728_set_scale(chan->channel, data, val, val2);
> +		if (ret)
> +			break;
> +
> +		ret = mcp4728_program_channel_cfg(chan->channel, indio_dev);
> +		break;
> +	default:
> +		ret = -EINVAL;
> +		break;
> +	}
> +
> +	return ret;
> +}



> +static int mcp4728_init_channels_data(struct mcp4728_data *data)
> +{
> +	u8 inbuf[MCP4728_READ_RESPONSE_LEN];
> +	int ret;
> +	unsigned int i;
> +
> +	ret = i2c_master_recv(data->client, inbuf, MCP4728_READ_RESPONSE_LEN);
> +	if (ret < 0) {
> +		dev_err(&data->client->dev,
> +			"failed to read mcp4728 conf. Err=%d\n", ret);
> +		return ret;

As this is only called from probe, we should still use dev_err_probe() in here
as mentioned below.


> +	} else if (ret != MCP4728_READ_RESPONSE_LEN) {
> +		dev_err(&data->client->dev,
> +			"failed to read mcp4728 conf. Wrong Response Len ret=%d\n",
> +			ret);
> +		return -EIO;
> +	}
> +
> +	for (i = 0; i < MCP4728_N_CHANNELS; i++) {
> +		struct mcp4728_channel_data *ch = &data->chdata[i];
> +		u8 r2				= inbuf[i * 6 + 1];
> +		u8 r3				= inbuf[i * 6 + 2];
> +
> +		ch->dac_value = FIELD_GET(MCP4728_DAC_H_MASK, r2) << 8 |
> +				FIELD_GET(MCP4728_DAC_L_MASK, r3);
> +		ch->ref_mode = FIELD_GET(MCP4728_VREF_MASK, r2);
> +		ch->pd_mode  = FIELD_GET(MCP4728_PDMODE_MASK, r2);
> +		ch->g_mode   = FIELD_GET(MCP4728_GAIN_MASK, r2);
> +	}
> +
> +	return 0;
> +}

...

> +static int mcp4728_probe(struct i2c_client *client)
> +{
> +	const struct i2c_device_id *id = i2c_client_get_device_id(client);
> +	struct mcp4728_data *data;
> +	struct iio_dev *indio_dev;
> +	int err;
> +
> +	indio_dev = devm_iio_device_alloc(&client->dev, sizeof(*data));
> +	if (!indio_dev)
> +		return -ENOMEM;
> +
> +	data = iio_priv(indio_dev);
> +	i2c_set_clientdata(client, indio_dev);
> +	data->client = client;
> +
> +	data->vdd_reg = devm_regulator_get(&client->dev, "vdd");
> +	if (IS_ERR(data->vdd_reg))
> +		return PTR_ERR(data->vdd_reg);
> +
> +	err = regulator_enable(data->vdd_reg);
> +	if (err)
> +		return err;
> +
> +	err = devm_add_action_or_reset(&client->dev, mcp4728_reg_disable,
> +				       data->vdd_reg);
> +	if (err)
> +		return err;
> +
> +	/* MCP4728 has internal EEPROM that save each channel boot configuration.

Trivial but comment syntax in IIO (there are some differences in a few other subsystems)
is
	/*
	 * MCP...

> +	 * It means that device configuration is unknown to the driver at kernel boot.
> +	 * mcp4728_init_channels_data reads back DAC settings and stores them in data
> +	 * structure.
> +	 */
> +	err = mcp4728_init_channels_data(data);
> +	if (err) {

I'd missed this previously but dev_err_probe() has several advantages in that
it handles deferring neatly and also ends up with less code.

> +		dev_err(&client->dev,
> +			"failed to read mcp4728 current configuration\n");
> +		return err;
> +	}
> +
> +	err = mcp4728_init_scales_avail(data);
> +	if (err) {
> +		dev_err(&client->dev, "failed to init scales\n");
> +		return err;
> +	}
> +
> +	indio_dev->name		= id->name;
> +	indio_dev->info		= &mcp4728_info;
> +	indio_dev->channels	= mcp4728_channels;
> +	indio_dev->num_channels = MCP4728_N_CHANNELS;
> +	indio_dev->modes	= INDIO_DIRECT_MODE;
> +
> +	return devm_iio_device_register(&client->dev, indio_dev);
> +}