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

Hi Jonathan,

I tested the driver and I didn't find any issue.

These are the tests I performed:

Test Configuration:
SW:
git://git.kernel.org/pub/scm/linux/kernel/git/jic23/iio.git
commit: ee812337ee74cc403b4fbd85840dbe1b21d9a60f

HW:
- Aster board from Toradex hosting imx7d processor
- Adafruit MCP4728 https://www.adafruit.com/product/4470

TEST:

Probe Test                                OK
#> insmod mcp4728.ko

Read Scales                                OK
~# cat /sys/devices/platform/soc/30800000.bus/30a50000.i2c/i2c-3/3-0064/iio:device1/out_voltage_scale_available
0.805664 0.500000 1.000000

Write DAC CH0                            OK
#>iio_attr -c mcp4728 voltage0 scale    1.000000
#>iio_attr -c mcp4728 voltage0 raw         750
Voltage Monitor Reading:                749 mV

Write DAC CH1                            OK
#>iio_attr -c mcp4728 voltage1 scale    0.5
#>iio_attr -c mcp4728 voltage1 raw        750
Voltage Monitor Reading:                378 mV

Write DAC CH2                            OK
#>iio_attr -c mcp4728 voltage2 scale    0.805664
#>iio_attr -c mcp4728 voltage2 raw        750
Voltage Monitor Reading:                603 mV ~ 750*0.805664 ~ 604 mV

Write DAC CH3                            OK
#>iio_attr -c mcp4728 voltage3 scale    1.000000
#>iio_attr -c mcp4728 voltage3 raw        350
Voltage Monitor Reading:                354 mV

Store EEPROM                            OK
#>echo y > /sys/devices/platform/soc/30800000.bus/30a50000.i2c/i2c-3/3-0064/iio:device1/store_eeprom
#>power cycle board
Voltage Monitor Reading CH0                749 mV
Voltage Monitor Reading CH1                378 mV
Voltage Monitor Reading CH2                605 mV
Voltage Monitor Reading CH3                355 mV

Power Down CH0
#>iio_attr -c mcp4728 voltage0 powerdown_mode 1kohm_to_gnd
#>iio_attr -c mcp4728 voltage0 powerdown 1
Voltage Monitor Reading CH0                 0 mV

Power Down CH1
#>iio_attr -c mcp4728 voltage1 powerdown_mode 1kohm_to_gnd
#>iio_attr -c mcp4728 voltage1 powerdown 1
Voltage Monitor Reading CH1                 0 mV

Power Down CH2
#>iio_attr -c mcp4728 voltage2 powerdown_mode 1kohm_to_gnd
#>iio_attr -c mcp4728 voltage2 powerdown 1
Voltage Monitor Reading CH2                 0 mV

Power Down CH3
#>iio_attr -c mcp4728 voltage3 powerdown_mode 1kohm_to_gnd
#>iio_attr -c mcp4728 voltage3 powerdown 1
Voltage Monitor Reading CH3                 0 mV


Regards

        Andrea

On 8/5/23 20:28, Jonathan Cameron wrote:

On Thu,  3 Aug 2023 14:56:35 +0200
Andrea Collamati [off-list ref] wrote:

quoted

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 <redacted>

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

quoted

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 @@

...

quoted

+
+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.

quoted

+}

...

quoted

+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.

quoted

+	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;
+}

quoted

+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.

quoted

+	} 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;
+}

...

quoted

+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...

quoted

+	 * 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.

quoted

+		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);
+}