[PATCH 1/3 v4] iio: magnetometer: ak8974: Correct realbits

[PATCH 1/3 v4] iio: magnetometer: ak8974: Correct realbits

[Linus Walleij]

The HSCDTD008A has 15 bits of actual ADC valie, and the
AMI305 and AMI306 has 12 bits.

Correct this by providing an extra parameter to the channel
macro and define a separate set of channels for each variant
of the chip. The resolution is the actual resolution of the
internal ADC of the chip.

The values are stored in a S16 in 2's complement so all 16
bits are used for storing (no shifting needed).

The AMI305, AMI306 and HSCDTD008A valid bits are picked from
respective datasheet.

My best educated guess is that AK8974 is also 12 bits. The
AK8973 is an 8 bit and earlier version, and the sibling
drivers AMI305 and AMI306 are 12 bits, so it makes sense
to assume that the AK8974 is also 12 bits.

Cc: Nick Reitemeyer <nick.reitemeyer@web.de>
Cc: Stephan Gerhold <stephan@gerhold.net>
Cc: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
ChangeLog v3->v4:
- Create two sets of channels for 12 or 16 bit mode.
ChangeLog v1->v3:
- New patch in the v3 patch set.
---
 drivers/iio/magnetometer/ak8974.c | 45 +++++++++++++++++++++++++------
 1 file changed, 37 insertions(+), 8 deletions(-)

diff --git a/drivers/iio/magnetometer/ak8974.c b/drivers/iio/magnetometer/ak8974.c
index ade4ed8f67d2..7d585c3b7e1e 100644
--- a/drivers/iio/magnetometer/ak8974.c
+++ b/drivers/iio/magnetometer/ak8974.c
@@ -651,7 +651,7 @@ static const struct iio_chan_spec_ext_info ak8974_ext_info[] = {
 	{ },
 };
 
-#define AK8974_AXIS_CHANNEL(axis, index)				\
+#define AK8974_AXIS_CHANNEL(axis, index, bits)				\
 	{								\
 		.type = IIO_MAGN,					\
 		.modified = 1,						\
@@ -662,16 +662,32 @@ static const struct iio_chan_spec_ext_info ak8974_ext_info[] = {
 		.scan_index = index,					\
 		.scan_type = {						\
 			.sign = 's',					\
-			.realbits = 16,					\
+			.realbits = bits,				\
 			.storagebits = 16,				\
 			.endianness = IIO_LE				\
 		},							\
 	}
 
-static const struct iio_chan_spec ak8974_channels[] = {
-	AK8974_AXIS_CHANNEL(X, 0),
-	AK8974_AXIS_CHANNEL(Y, 1),
-	AK8974_AXIS_CHANNEL(Z, 2),
+/*
+ * We have no datasheet for the AK8974 but we guess that its
+ * ADC is 12 bits. The AMI305 and AMI306 certainly has 12bit
+ * ADC.
+ */
+static const struct iio_chan_spec ak8974_12_bits_channels[] = {
+	AK8974_AXIS_CHANNEL(X, 0, 12),
+	AK8974_AXIS_CHANNEL(Y, 1, 12),
+	AK8974_AXIS_CHANNEL(Z, 2, 12),
+	IIO_CHAN_SOFT_TIMESTAMP(3),
+};
+
+/*
+ * The HSCDTD008A has 15 bits resolution the way we set it up
+ * in CTRL4.
+ */
+static const struct iio_chan_spec ak8974_15_bits_channels[] = {
+	AK8974_AXIS_CHANNEL(X, 0, 15),
+	AK8974_AXIS_CHANNEL(Y, 1, 15),
+	AK8974_AXIS_CHANNEL(Z, 2, 15),
 	IIO_CHAN_SOFT_TIMESTAMP(3),
 };
 
@@ -815,8 +831,21 @@ static int ak8974_probe(struct i2c_client *i2c,
 	pm_runtime_put(&i2c->dev);
 
 	indio_dev->dev.parent = &i2c->dev;
-	indio_dev->channels = ak8974_channels;
-	indio_dev->num_channels = ARRAY_SIZE(ak8974_channels);
+	switch (ak8974->variant) {
+	case AK8974_WHOAMI_VALUE_AMI306:
+	case AK8974_WHOAMI_VALUE_AMI305:
+		indio_dev->channels = ak8974_12_bits_channels;
+		indio_dev->num_channels = ARRAY_SIZE(ak8974_12_bits_channels);
+		break;
+	case AK8974_WHOAMI_VALUE_HSCDTD008A:
+		indio_dev->channels = ak8974_15_bits_channels;
+		indio_dev->num_channels = ARRAY_SIZE(ak8974_15_bits_channels);
+		break;
+	default:
+		indio_dev->channels = ak8974_12_bits_channels;
+		indio_dev->num_channels = ARRAY_SIZE(ak8974_12_bits_channels);
+		break;
+	}
 	indio_dev->info = &ak8974_info;
 	indio_dev->available_scan_masks = ak8974_scan_masks;
 	indio_dev->modes = INDIO_DIRECT_MODE;
-- 
2.21.1

[PATCH 2/3 v4] iio: magnetometer: ak8974: Break out measurement

[Linus Walleij]

This breaks out the measurement code to its own function
so we can handle this without swirling it up with the
big switch() statement inside ak8974_read_raw().

Keep a local s16 helper variable for the signed value
coming out of the measurement before assigning it to the
integer *val. The local variable makes the code easier
to read and the compiler will optimize it if possible.

Cc: Nick Reitemeyer <nick.reitemeyer@web.de>
Cc: Stephan Gerhold <stephan@gerhold.net>
Reviewed-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
ChangeLog v3->v4:
- Assign the casted s16 to the int *val.
- Collect Michał's review tag.
ChangeLog v2->v3:
- Return directly from the raw read function, we
  need no goto:s as we got rid of the lock.
- Change the measurement function to return an int *
  after measurement and just pass *val
  to the function saving a local variable.
- Insert a comment explaining the explicit cast to
  (s16).
- Rename function as ak8974_measure_channel() so the
  name states exactly what is going on.
- Break out as a separate patch.
---
 drivers/iio/magnetometer/ak8974.c | 66 +++++++++++++++++++------------
 1 file changed, 40 insertions(+), 26 deletions(-)

diff --git a/drivers/iio/magnetometer/ak8974.c b/drivers/iio/magnetometer/ak8974.c
index 7d585c3b7e1e..fb6d84b79a7a 100644
--- a/drivers/iio/magnetometer/ak8974.c
+++ b/drivers/iio/magnetometer/ak8974.c
@@ -554,47 +554,61 @@ static int ak8974_detect(struct ak8974 *ak8974)
 	return 0;
 }
 
+static int ak8974_measure_channel(struct ak8974 *ak8974, unsigned long address,
+				  int *val)
+{
+	__le16 hw_values[3];
+	int ret;
+
+	pm_runtime_get_sync(&ak8974->i2c->dev);
+	mutex_lock(&ak8974->lock);
+
+	/*
+	 * We read all axes and discard all but one, for optimized
+	 * reading, use the triggered buffer.
+	 */
+	ret = ak8974_trigmeas(ak8974);
+	if (ret)
+		goto out_unlock;
+	ret = ak8974_getresult(ak8974, hw_values);
+	if (ret)
+		goto out_unlock;
+	/*
+	 * This explicit cast to (s16) is necessary as the measurement
+	 * is done in 2's complement with positive and negative values.
+	 * The follwing assignment to *val will then convert the signed
+	 * s16 value to a signed int value.
+	 */
+	*val = (s16)le16_to_cpu(hw_values[address]);
+out_unlock:
+	mutex_unlock(&ak8974->lock);
+	pm_runtime_mark_last_busy(&ak8974->i2c->dev);
+	pm_runtime_put_autosuspend(&ak8974->i2c->dev);
+
+	return ret;
+}
+
 static int ak8974_read_raw(struct iio_dev *indio_dev,
 			   struct iio_chan_spec const *chan,
 			   int *val, int *val2,
 			   long mask)
 {
 	struct ak8974 *ak8974 = iio_priv(indio_dev);
-	__le16 hw_values[3];
-	int ret = -EINVAL;
-
-	pm_runtime_get_sync(&ak8974->i2c->dev);
-	mutex_lock(&ak8974->lock);
+	int ret;
 
 	switch (mask) {
 	case IIO_CHAN_INFO_RAW:
 		if (chan->address > 2) {
 			dev_err(&ak8974->i2c->dev, "faulty channel address\n");
-			ret = -EIO;
-			goto out_unlock;
+			return -EIO;
 		}
-		ret = ak8974_trigmeas(ak8974);
+		ret = ak8974_measure_channel(ak8974, chan->address, val);
 		if (ret)
-			goto out_unlock;
-		ret = ak8974_getresult(ak8974, hw_values);
-		if (ret)
-			goto out_unlock;
-
-		/*
-		 * We read all axes and discard all but one, for optimized
-		 * reading, use the triggered buffer.
-		 */
-		*val = (s16)le16_to_cpu(hw_values[chan->address]);
-
-		ret = IIO_VAL_INT;
+			return ret;
+		return IIO_VAL_INT;
 	}
 
- out_unlock:
-	mutex_unlock(&ak8974->lock);
-	pm_runtime_mark_last_busy(&ak8974->i2c->dev);
-	pm_runtime_put_autosuspend(&ak8974->i2c->dev);
-
-	return ret;
+	return -EINVAL;
 }
 
 static void ak8974_fill_buffer(struct iio_dev *indio_dev)
-- 
2.21.1

[PATCH 3/3 v4] iio: magnetometer: ak8974: Provide scaling

[Linus Walleij]

The manual for the HSCDTD008A gives us a scaling for the
three axis as +/- 2.4mT (24 Gauss) per axis.

The manual for the AMI305 and AMI306 gives us a scaling
for the three axis as +/- 12 Gauss per axis.

Tests with the HSCDTD008A sensor, cat the raw values:
$ cat in_magn_*_raw
raw
45
189
-19

The scaling factor in in_magn_*_scale is 0.001464843,
which gives:
0.065 Gauss
0.277 Gauss
-0.027 Gauss

The earths magnetic field is in the range of 0.25 to 0.65
Gauss on the surface according to Wikipedia, so these
seem like reasonable values.

Again we are guessing that the AK8974 has a 12 bit ADC,
based on the similarity with AMI305 and AMI306.

Cc: Nick Reitemeyer <nick.reitemeyer@web.de>
Cc: Stephan Gerhold <stephan@gerhold.net>
Cc: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
ChangeLog v3->v4:
- Do not multiply the range with 2, instead divide by
  two in divisor and dividend. (Thus it becomes 2^11
  and 2^14 respectively.)
- Use the IIO_VAL_FRACTIONAL_LOG2 trick and pass 2^11
  or 2^14 as range.
ChangeLog v2->v3:
- Scale the 2.4mT/24Gauss to 15 bits for the HSCDTD008A.
- Scale the 12 Gauss to 12 bits for the AMI305/AMI306
- Use 12 bits for the other variants.
- Return directly in the raw read function.
ChangeLog v1->v2:
- Split out the measurement refactoring.
---
 drivers/iio/magnetometer/ak8974.c | 45 ++++++++++++++++++++++++++++++-
 1 file changed, 44 insertions(+), 1 deletion(-)

diff --git a/drivers/iio/magnetometer/ak8974.c b/drivers/iio/magnetometer/ak8974.c
index fb6d84b79a7a..2d500be9da40 100644
--- a/drivers/iio/magnetometer/ak8974.c
+++ b/drivers/iio/magnetometer/ak8974.c
@@ -606,6 +606,48 @@ static int ak8974_read_raw(struct iio_dev *indio_dev,
 		if (ret)
 			return ret;
 		return IIO_VAL_INT;
+	case IIO_CHAN_INFO_SCALE:
+		switch (ak8974->variant) {
+		case AK8974_WHOAMI_VALUE_AMI306:
+		case AK8974_WHOAMI_VALUE_AMI305:
+			/*
+			 * The datasheet for AMI305 and AMI306, page 6
+			 * specifies the range of the sensor to be
+			 * +/- 12 Gauss.
+			 */
+			*val = 12;
+			/*
+			 * 12 bits are used, +/- 2^11
+			 * [ -2048 .. 2047 ] (manual page 20)
+			 * [ 0xf800 .. 0x07ff ]
+			 */
+			*val2 = 11;
+			return IIO_VAL_FRACTIONAL_LOG2;
+		case AK8974_WHOAMI_VALUE_HSCDTD008A:
+			/*
+			 * The datasheet for HSCDTF008A, page 3 specifies the
+			 * range of the sensor as +/- 2.4 mT per axis, which
+			 * corresponds to +/- 2400 uT = +/- 24 Gauss.
+			 */
+			*val = 24;
+			/*
+			 * 15 bits are used (set up in CTRL4), +/- 2^14
+			 * [ -16384 .. 16383 ] (manual page 24)
+			 * [ 0xc000 .. 0x3fff ]
+			 */
+			*val2 = 14;
+			return IIO_VAL_FRACTIONAL_LOG2;
+		default:
+			/* GUESSING +/- 12 Gauss */
+			*val = 12;
+			/* GUESSING 12 bits ADC +/- 2^11 */
+			*val2 = 11;
+			return IIO_VAL_FRACTIONAL_LOG2;
+		}
+		break;
+	default:
+		/* Unknown request */
+		break;
 	}
 
 	return -EINVAL;
@@ -670,7 +712,8 @@ static const struct iio_chan_spec_ext_info ak8974_ext_info[] = {
 		.type = IIO_MAGN,					\
 		.modified = 1,						\
 		.channel2 = IIO_MOD_##axis,				\
-		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),		\
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |		\
+			BIT(IIO_CHAN_INFO_SCALE),			\
 		.ext_info = ak8974_ext_info,				\
 		.address = index,					\
 		.scan_index = index,					\
-- 
2.21.1

Re: [PATCH 3/3 v4] iio: magnetometer: ak8974: Provide scaling

[Jonathan Cameron]

On Mon, 20 Apr 2020 22:40:22 +0200
Linus Walleij <linus.walleij@linaro.org> wrote:

> The manual for the HSCDTD008A gives us a scaling for the
> three axis as +/- 2.4mT (24 Gauss) per axis.
> 
> The manual for the AMI305 and AMI306 gives us a scaling
> for the three axis as +/- 12 Gauss per axis.
> 
> Tests with the HSCDTD008A sensor, cat the raw values:
> $ cat in_magn_*_raw
> raw
> 45
> 189
> -19
> 
> The scaling factor in in_magn_*_scale is 0.001464843,
> which gives:
> 0.065 Gauss
> 0.277 Gauss
> -0.027 Gauss
> 
> The earths magnetic field is in the range of 0.25 to 0.65
> Gauss on the surface according to Wikipedia, so these
> seem like reasonable values.
> 
> Again we are guessing that the AK8974 has a 12 bit ADC,
> based on the similarity with AMI305 and AMI306.
> 
> Cc: Nick Reitemeyer <nick.reitemeyer@web.de>
> Cc: Stephan Gerhold <stephan@gerhold.net>
> Cc: Michał Mirosław <mirq-linux@rere.qmqm.pl>
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Applied, but they'll sit in my testing branch for a while yet
most likely so can rebase (add tags / drop them etc) if others
still wish to comment.

Thanks,

Jonathan

> ---
> ChangeLog v3->v4:
> - Do not multiply the range with 2, instead divide by
>   two in divisor and dividend. (Thus it becomes 2^11
>   and 2^14 respectively.)
> - Use the IIO_VAL_FRACTIONAL_LOG2 trick and pass 2^11
>   or 2^14 as range.
> ChangeLog v2->v3:
> - Scale the 2.4mT/24Gauss to 15 bits for the HSCDTD008A.
> - Scale the 12 Gauss to 12 bits for the AMI305/AMI306
> - Use 12 bits for the other variants.
> - Return directly in the raw read function.
> ChangeLog v1->v2:
> - Split out the measurement refactoring.
> ---
>  drivers/iio/magnetometer/ak8974.c | 45 ++++++++++++++++++++++++++++++-
>  1 file changed, 44 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/magnetometer/ak8974.c b/drivers/iio/magnetometer/ak8974.c
> index fb6d84b79a7a..2d500be9da40 100644
> --- a/drivers/iio/magnetometer/ak8974.c
> +++ b/drivers/iio/magnetometer/ak8974.c
> @@ -606,6 +606,48 @@ static int ak8974_read_raw(struct iio_dev *indio_dev,
>  		if (ret)
>  			return ret;
>  		return IIO_VAL_INT;
> +	case IIO_CHAN_INFO_SCALE:
> +		switch (ak8974->variant) {
> +		case AK8974_WHOAMI_VALUE_AMI306:
> +		case AK8974_WHOAMI_VALUE_AMI305:
> +			/*
> +			 * The datasheet for AMI305 and AMI306, page 6
> +			 * specifies the range of the sensor to be
> +			 * +/- 12 Gauss.
> +			 */
> +			*val = 12;
> +			/*
> +			 * 12 bits are used, +/- 2^11
> +			 * [ -2048 .. 2047 ] (manual page 20)
> +			 * [ 0xf800 .. 0x07ff ]
> +			 */
> +			*val2 = 11;
> +			return IIO_VAL_FRACTIONAL_LOG2;
> +		case AK8974_WHOAMI_VALUE_HSCDTD008A:
> +			/*
> +			 * The datasheet for HSCDTF008A, page 3 specifies the
> +			 * range of the sensor as +/- 2.4 mT per axis, which
> +			 * corresponds to +/- 2400 uT = +/- 24 Gauss.
> +			 */
> +			*val = 24;
> +			/*
> +			 * 15 bits are used (set up in CTRL4), +/- 2^14
> +			 * [ -16384 .. 16383 ] (manual page 24)
> +			 * [ 0xc000 .. 0x3fff ]
> +			 */
> +			*val2 = 14;
> +			return IIO_VAL_FRACTIONAL_LOG2;
> +		default:
> +			/* GUESSING +/- 12 Gauss */
> +			*val = 12;
> +			/* GUESSING 12 bits ADC +/- 2^11 */
> +			*val2 = 11;
> +			return IIO_VAL_FRACTIONAL_LOG2;
> +		}
> +		break;
> +	default:
> +		/* Unknown request */
> +		break;
>  	}
>  
>  	return -EINVAL;
> @@ -670,7 +712,8 @@ static const struct iio_chan_spec_ext_info ak8974_ext_info[] = {
>  		.type = IIO_MAGN,					\
>  		.modified = 1,						\
>  		.channel2 = IIO_MOD_##axis,				\
> -		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),		\
> +		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |		\
> +			BIT(IIO_CHAN_INFO_SCALE),			\
>  		.ext_info = ak8974_ext_info,				\
>  		.address = index,					\
>  		.scan_index = index,					\