[PATCH] iio: kx022a: Fix acceleration value scaling

[PATCH] iio: kx022a: Fix acceleration value scaling

[Matti Vaittinen]

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The IIO ABI mandates acceleration values from accelerometer to be
emitted in m/s^2. The KX022A was emitting values in micro m/s^2.

Fix driver to report the correct scale values.

Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
Reported-by: Jagath Jog J <jagathjog1996@gmail.com>
Fixes: 7c1d1677b322 ("iio: accel: Support Kionix/ROHM KX022A accelerometer")

---
The fix is somewhat crude and just crops the last 3 digits (rounds) of the
scale while using IIO_VAL_INT_PLUS_NANO. I played with a thought of using
IIO_VAL_FRACTIONAL, which could have modelled the computation
G_range * g * scaling / (2^16 * scaling) - where scaling 10000 would
have allowed using g value 980665.

This would have worked fine for reporting scale and available scales -
but would be somewhat tricky when converting the user-supplied scale to
register values in write_raw().

Well, the g varies from 9.832 (poles) to 9.780 (equator) according to
some website - no proper source check done but this sounds about right -
so maybe the loss of accuracy is acceptable.

I did only very quick testing on KX022A and iio_generic_buffer. After
the patch the values seemed to be correct order of magnitude. Further
testing is appreciated :)

---
 drivers/iio/accel/kionix-kx022a.c | 37 ++++++++++++++++++++++---------
 1 file changed, 26 insertions(+), 11 deletions(-)

diff --git a/drivers/iio/accel/kionix-kx022a.c b/drivers/iio/accel/kionix-kx022a.c
index 4ea3c6718ed4..971fc60efef0 100644
--- a/drivers/iio/accel/kionix-kx022a.c
+++ b/drivers/iio/accel/kionix-kx022a.c
@@ -273,17 +273,17 @@ static const unsigned int kx022a_odrs[] = {
  *	(range / 2^bits) * g = (range / 2^bits) * 9.80665 m/s^2
  *	=> KX022A uses 16 bit (HiRes mode - assume the low 8 bits are zeroed
  *	in low-power mode(?) )
- *	=> +/-2G  => 4 / 2^16 * 9,80665 * 10^6 (to scale to micro)
- *	=> +/-2G  - 598.550415
- *	   +/-4G  - 1197.10083
- *	   +/-8G  - 2394.20166
- *	   +/-16G - 4788.40332
+ *	=> +/-2G  => 4 / 2^16 * 9,80665
+ *	=> +/-2G  - 0.000598550415
+ *	   +/-4G  - 0.00119710083
+ *	   +/-8G  - 0.00239420166
+ *	   +/-16G - 0.00478840332
  */
 static const int kx022a_scale_table[][2] = {
-	{ 598, 550415 },
-	{ 1197, 100830 },
-	{ 2394, 201660 },
-	{ 4788, 403320 },
+	{ 0, 598550 },
+	{ 0, 1197101 },
+	{ 0, 2394202 },
+	{ 0, 4788403 },
 };
 
 static int kx022a_read_avail(struct iio_dev *indio_dev,
@@ -302,7 +302,7 @@ static int kx022a_read_avail(struct iio_dev *indio_dev,
 		*vals = (const int *)kx022a_scale_table;
 		*length = ARRAY_SIZE(kx022a_scale_table) *
 			  ARRAY_SIZE(kx022a_scale_table[0]);
-		*type = IIO_VAL_INT_PLUS_MICRO;
+		*type = IIO_VAL_INT_PLUS_NANO;
 		return IIO_AVAIL_LIST;
 	default:
 		return -EINVAL;
@@ -366,6 +366,20 @@ static int kx022a_turn_on_unlock(struct kx022a_data *data)
 	return ret;
 }
 
+static int kx022a_write_raw_get_fmt(struct iio_dev *idev,
+				    struct iio_chan_spec const *chan,
+				    long mask)
+{
+	switch (mask) {
+	case IIO_CHAN_INFO_SCALE:
+		return IIO_VAL_INT_PLUS_NANO;
+	case IIO_CHAN_INFO_SAMP_FREQ:
+		return IIO_VAL_INT_PLUS_MICRO;
+	default:
+		return -EINVAL;
+	}
+}
+
 static int kx022a_write_raw(struct iio_dev *idev,
 			    struct iio_chan_spec const *chan,
 			    int val, int val2, long mask)
@@ -510,7 +524,7 @@ static int kx022a_read_raw(struct iio_dev *idev,
 
 		kx022a_reg2scale(regval, val, val2);
 
-		return IIO_VAL_INT_PLUS_MICRO;
+		return IIO_VAL_INT_PLUS_NANO;
 	}
 
 	return -EINVAL;
@@ -712,6 +726,7 @@ static int kx022a_fifo_flush(struct iio_dev *idev, unsigned int samples)
 static const struct iio_info kx022a_info = {
 	.read_raw = &kx022a_read_raw,
 	.write_raw = &kx022a_write_raw,
+	.write_raw_get_fmt = &kx022a_write_raw_get_fmt,
 	.read_avail = &kx022a_read_avail,
 
 	.validate_trigger	= iio_validate_own_trigger,
-- 
2.41.0


-- 
Matti Vaittinen, Linux device drivers
ROHM Semiconductors, Finland SWDC
Kiviharjunlenkki 1E
90220 OULU
FINLAND

~~~ "I don't think so," said Rene Descartes. Just then he vanished ~~~
Simon says - in Latin please.
~~~ "non cogito me" dixit Rene Descarte, deinde evanescavit ~~~
Thanks to Simon Glass for the translation =] 

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Re: [PATCH] iio: kx022a: Fix acceleration value scaling

[Jagath Jog J]

Hi Matti,

On Thu, Oct 19, 2023 at 6:54 PM Matti Vaittinen
<mazziesaccount@gmail.com> wrote:
>
> The IIO ABI mandates acceleration values from accelerometer to be
> emitted in m/s^2. The KX022A was emitting values in micro m/s^2.
>
> Fix driver to report the correct scale values.
>
> Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
> Reported-by: Jagath Jog J <jagathjog1996@gmail.com>
> Fixes: 7c1d1677b322 ("iio: accel: Support Kionix/ROHM KX022A accelerometer")
>
> ---
> The fix is somewhat crude and just crops the last 3 digits (rounds) of the
> scale while using IIO_VAL_INT_PLUS_NANO. I played with a thought of using
> IIO_VAL_FRACTIONAL, which could have modelled the computation
> G_range * g * scaling / (2^16 * scaling) - where scaling 10000 would
> have allowed using g value 980665.
>
> This would have worked fine for reporting scale and available scales -
> but would be somewhat tricky when converting the user-supplied scale to
> register values in write_raw().
>
> Well, the g varies from 9.832 (poles) to 9.780 (equator) according to
> some website - no proper source check done but this sounds about right -
> so maybe the loss of accuracy is acceptable.
>
> I did only very quick testing on KX022A and iio_generic_buffer. After
> the patch the values seemed to be correct order of magnitude. Further
> testing is appreciated :)

Values are correct with this change, Thank you for fixing.
Tested-by: Jagath Jog J <jagathjog1996@gmail.com>

Regards
Jagath


>
> ---
>  drivers/iio/accel/kionix-kx022a.c | 37 ++++++++++++++++++++++---------
>  1 file changed, 26 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/iio/accel/kionix-kx022a.c b/drivers/iio/accel/kionix-kx022a.c
> index 4ea3c6718ed4..971fc60efef0 100644
> --- a/drivers/iio/accel/kionix-kx022a.c
> +++ b/drivers/iio/accel/kionix-kx022a.c
> @@ -273,17 +273,17 @@ static const unsigned int kx022a_odrs[] = {
>   *     (range / 2^bits) * g = (range / 2^bits) * 9.80665 m/s^2
>   *     => KX022A uses 16 bit (HiRes mode - assume the low 8 bits are zeroed
>   *     in low-power mode(?) )
> - *     => +/-2G  => 4 / 2^16 * 9,80665 * 10^6 (to scale to micro)
> - *     => +/-2G  - 598.550415
> - *        +/-4G  - 1197.10083
> - *        +/-8G  - 2394.20166
> - *        +/-16G - 4788.40332
> + *     => +/-2G  => 4 / 2^16 * 9,80665
> + *     => +/-2G  - 0.000598550415
> + *        +/-4G  - 0.00119710083
> + *        +/-8G  - 0.00239420166
> + *        +/-16G - 0.00478840332
>   */
>  static const int kx022a_scale_table[][2] = {
> -       { 598, 550415 },
> -       { 1197, 100830 },
> -       { 2394, 201660 },
> -       { 4788, 403320 },
> +       { 0, 598550 },
> +       { 0, 1197101 },
> +       { 0, 2394202 },
> +       { 0, 4788403 },
>  };
>
>  static int kx022a_read_avail(struct iio_dev *indio_dev,
> @@ -302,7 +302,7 @@ static int kx022a_read_avail(struct iio_dev *indio_dev,
>                 *vals = (const int *)kx022a_scale_table;
>                 *length = ARRAY_SIZE(kx022a_scale_table) *
>                           ARRAY_SIZE(kx022a_scale_table[0]);
> -               *type = IIO_VAL_INT_PLUS_MICRO;
> +               *type = IIO_VAL_INT_PLUS_NANO;
>                 return IIO_AVAIL_LIST;
>         default:
>                 return -EINVAL;
> @@ -366,6 +366,20 @@ static int kx022a_turn_on_unlock(struct kx022a_data *data)
>         return ret;
>  }
>
> +static int kx022a_write_raw_get_fmt(struct iio_dev *idev,
> +                                   struct iio_chan_spec const *chan,
> +                                   long mask)
> +{
> +       switch (mask) {
> +       case IIO_CHAN_INFO_SCALE:
> +               return IIO_VAL_INT_PLUS_NANO;
> +       case IIO_CHAN_INFO_SAMP_FREQ:
> +               return IIO_VAL_INT_PLUS_MICRO;
> +       default:
> +               return -EINVAL;
> +       }
> +}
> +
>  static int kx022a_write_raw(struct iio_dev *idev,
>                             struct iio_chan_spec const *chan,
>                             int val, int val2, long mask)
> @@ -510,7 +524,7 @@ static int kx022a_read_raw(struct iio_dev *idev,
>
>                 kx022a_reg2scale(regval, val, val2);
>
> -               return IIO_VAL_INT_PLUS_MICRO;
> +               return IIO_VAL_INT_PLUS_NANO;
>         }
>
>         return -EINVAL;
> @@ -712,6 +726,7 @@ static int kx022a_fifo_flush(struct iio_dev *idev, unsigned int samples)
>  static const struct iio_info kx022a_info = {
>         .read_raw = &kx022a_read_raw,
>         .write_raw = &kx022a_write_raw,
> +       .write_raw_get_fmt = &kx022a_write_raw_get_fmt,
>         .read_avail = &kx022a_read_avail,
>
>         .validate_trigger       = iio_validate_own_trigger,
> --
> 2.41.0
>
>
> --
> Matti Vaittinen, Linux device drivers
> ROHM Semiconductors, Finland SWDC
> Kiviharjunlenkki 1E
> 90220 OULU
> FINLAND
>
> ~~~ "I don't think so," said Rene Descartes. Just then he vanished ~~~
> Simon says - in Latin please.
> ~~~ "non cogito me" dixit Rene Descarte, deinde evanescavit ~~~
> Thanks to Simon Glass for the translation =]

Re: [PATCH] iio: kx022a: Fix acceleration value scaling

[Matti Vaittinen]

On 10/19/23 21:21, Jagath Jog J wrote:
> Hi Matti,
> 
> On Thu, Oct 19, 2023 at 6:54 PM Matti Vaittinen
> <mazziesaccount@gmail.com> wrote:
>>
>> The IIO ABI mandates acceleration values from accelerometer to be
>> emitted in m/s^2. The KX022A was emitting values in micro m/s^2.
>>
>> Fix driver to report the correct scale values.
>>
>> Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
>> Reported-by: Jagath Jog J <jagathjog1996@gmail.com>
>> Fixes: 7c1d1677b322 ("iio: accel: Support Kionix/ROHM KX022A accelerometer")
>>
>> ---
>> The fix is somewhat crude and just crops the last 3 digits (rounds) of the
>> scale while using IIO_VAL_INT_PLUS_NANO. I played with a thought of using
>> IIO_VAL_FRACTIONAL, which could have modelled the computation
>> G_range * g * scaling / (2^16 * scaling) - where scaling 10000 would
>> have allowed using g value 980665.
>>
>> This would have worked fine for reporting scale and available scales -
>> but would be somewhat tricky when converting the user-supplied scale to
>> register values in write_raw().
>>
>> Well, the g varies from 9.832 (poles) to 9.780 (equator) according to
>> some website - no proper source check done but this sounds about right -
>> so maybe the loss of accuracy is acceptable.
>>
>> I did only very quick testing on KX022A and iio_generic_buffer. After
>> the patch the values seemed to be correct order of magnitude. Further
>> testing is appreciated :)
> 
> Values are correct with this change, Thank you for fixing.
> Tested-by: Jagath Jog J <jagathjog1996@gmail.com>

Thanks a ton for testing! May I ask which component did you use (or did 
you just use some 'simulated' regster values?)

Yours,
	-- Matti

-- 
Matti Vaittinen
Linux kernel developer at ROHM Semiconductors
Oulu Finland

~~ When things go utterly wrong vim users can always type :help! ~~

Re: [PATCH] iio: kx022a: Fix acceleration value scaling

[Jagath Jog J]

On Fri, Oct 20, 2023 at 5:39 PM Matti Vaittinen
<mazziesaccount@gmail.com> wrote:
>
> On 10/19/23 21:21, Jagath Jog J wrote:
> > Hi Matti,
> >
> > On Thu, Oct 19, 2023 at 6:54 PM Matti Vaittinen
> > <mazziesaccount@gmail.com> wrote:
> >>

> >> I did only very quick testing on KX022A and iio_generic_buffer. After
> >> the patch the values seemed to be correct order of magnitude. Further
> >> testing is appreciated :)
> >
> > Values are correct with this change, Thank you for fixing.
> > Tested-by: Jagath Jog J <jagathjog1996@gmail.com>
>
> Thanks a ton for testing! May I ask which component did you use (or did
> you just use some 'simulated' regster values?)

Hi Matti,

I just simulated with the register values, Should the 'tested-by' tag only be
provided after hardware testing? I referred to this driver because it's
the most recent accelerometer driver that was merged.

Regards
Jagath

Re: [PATCH] iio: kx022a: Fix acceleration value scaling

[Matti Vaittinen]

On 10/20/23 19:48, Jagath Jog J wrote:
> On Fri, Oct 20, 2023 at 5:39 PM Matti Vaittinen
> <mazziesaccount@gmail.com> wrote:
>>
>> On 10/19/23 21:21, Jagath Jog J wrote:
>>> Hi Matti,
>>>
>>> On Thu, Oct 19, 2023 at 6:54 PM Matti Vaittinen
>>> <mazziesaccount@gmail.com> wrote:
>>>>
> 
>>>> I did only very quick testing on KX022A and iio_generic_buffer. After
>>>> the patch the values seemed to be correct order of magnitude. Further
>>>> testing is appreciated :)
>>>
>>> Values are correct with this change, Thank you for fixing.
>>> Tested-by: Jagath Jog J <jagathjog1996@gmail.com>
>>
>> Thanks a ton for testing! May I ask which component did you use (or did
>> you just use some 'simulated' regster values?)
> 
> Hi Matti,
> 
> I just simulated with the register values, Should the 'tested-by' tag only be
> provided after hardware testing?

I am not sure TBH. I didn't have a problem with your tag though, I was 
merely curious to hear about the IC usage :)

Now that you mentioned the tested-by tag usage, I started to wonder it 
as well. From pure SW/driver point of view the register value simulation 
is sufficient - but in practice we are not interested in whether the 
code works "in theory" - but whether the products do really work. This 
is something which includes handling of potential HW quircks and 
oddities - which are not always documented or known.

If we assume a case where someone is developing new gizmo and hits a bug 
which is in reality caused by some undocumented HW hiccup - then fixes 
with "tested-by" tags which are not actually tested on HW having this 
hiccup but using SW simulation - may be misleading.

The above is just some overall pondering - I am not too concerned on 
your tested-by tag :) Besides, it's cool you did the testing! I 
appreciate that! However, I wonder if there is some wider consensus 
whether the tests should be ran using real HW when tested-by tag is 
given. Jonathan, do you have any educated opinion on this?

> I referred to this driver because it's
> the most recent accelerometer driver that was merged.

Makes sense :) Thanks for replying!

Yours,
	-- Matti

-- 
Matti Vaittinen
Linux kernel developer at ROHM Semiconductors
Oulu Finland

~~ When things go utterly wrong vim users can always type :help! ~~

Re: [PATCH] iio: kx022a: Fix acceleration value scaling

[Jonathan Cameron]

On Thu, 19 Oct 2023 16:23:56 +0300
Matti Vaittinen <mazziesaccount@gmail.com> wrote:

> The IIO ABI mandates acceleration values from accelerometer to be
> emitted in m/s^2. The KX022A was emitting values in micro m/s^2.
> 
> Fix driver to report the correct scale values.
> 
> Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
> Reported-by: Jagath Jog J <jagathjog1996@gmail.com>
> Fixes: 7c1d1677b322 ("iio: accel: Support Kionix/ROHM KX022A accelerometer")
> 
> ---
> The fix is somewhat crude and just crops the last 3 digits (rounds) of the
> scale while using IIO_VAL_INT_PLUS_NANO. I played with a thought of using
> IIO_VAL_FRACTIONAL, which could have modelled the computation
> G_range * g * scaling / (2^16 * scaling) - where scaling 10000 would
> have allowed using g value 980665.
> 
> This would have worked fine for reporting scale and available scales -
> but would be somewhat tricky when converting the user-supplied scale to
> register values in write_raw().
> 
> Well, the g varies from 9.832 (poles) to 9.780 (equator) according to
> some website - no proper source check done but this sounds about right -
> so maybe the loss of accuracy is acceptable.

MEMS accelerometers tend to be pretty inaccurate. So I'd not worry too much about
this loss of accuracy at all.
The 0 point according to the datasheet I just looked at is +- 25mg and
if I read the sensitivity numbers right part to part variation in scale
is well above 5%.  For 2G mode, it lists acceptable 1G values of
min=15401, typical=16384, max=17367

So if anyone actually wants to do precision measurement they need to calibrate
their particular device + deal with the variation due to temperature etc
which makes this even more fun.

Applied to my local fixes-togreg branch of iio.git, but I've just sent a pull request
so this may not go out until after the 6.7 merge window.

Jonathan

> 
> I did only very quick testing on KX022A and iio_generic_buffer. After
> the patch the values seemed to be correct order of magnitude. Further
> testing is appreciated :)
> 
> ---
>  drivers/iio/accel/kionix-kx022a.c | 37 ++++++++++++++++++++++---------
>  1 file changed, 26 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/iio/accel/kionix-kx022a.c b/drivers/iio/accel/kionix-kx022a.c
> index 4ea3c6718ed4..971fc60efef0 100644
> --- a/drivers/iio/accel/kionix-kx022a.c
> +++ b/drivers/iio/accel/kionix-kx022a.c
> @@ -273,17 +273,17 @@ static const unsigned int kx022a_odrs[] = {
>   *	(range / 2^bits) * g = (range / 2^bits) * 9.80665 m/s^2
>   *	=> KX022A uses 16 bit (HiRes mode - assume the low 8 bits are zeroed
>   *	in low-power mode(?) )
> - *	=> +/-2G  => 4 / 2^16 * 9,80665 * 10^6 (to scale to micro)
> - *	=> +/-2G  - 598.550415
> - *	   +/-4G  - 1197.10083
> - *	   +/-8G  - 2394.20166
> - *	   +/-16G - 4788.40332
> + *	=> +/-2G  => 4 / 2^16 * 9,80665
> + *	=> +/-2G  - 0.000598550415
> + *	   +/-4G  - 0.00119710083
> + *	   +/-8G  - 0.00239420166
> + *	   +/-16G - 0.00478840332
>   */
>  static const int kx022a_scale_table[][2] = {
> -	{ 598, 550415 },
> -	{ 1197, 100830 },
> -	{ 2394, 201660 },
> -	{ 4788, 403320 },
> +	{ 0, 598550 },
> +	{ 0, 1197101 },
> +	{ 0, 2394202 },
> +	{ 0, 4788403 },
>  };
>  
>  static int kx022a_read_avail(struct iio_dev *indio_dev,
> @@ -302,7 +302,7 @@ static int kx022a_read_avail(struct iio_dev *indio_dev,
>  		*vals = (const int *)kx022a_scale_table;
>  		*length = ARRAY_SIZE(kx022a_scale_table) *
>  			  ARRAY_SIZE(kx022a_scale_table[0]);
> -		*type = IIO_VAL_INT_PLUS_MICRO;
> +		*type = IIO_VAL_INT_PLUS_NANO;
>  		return IIO_AVAIL_LIST;
>  	default:
>  		return -EINVAL;
> @@ -366,6 +366,20 @@ static int kx022a_turn_on_unlock(struct kx022a_data *data)
>  	return ret;
>  }
>  
> +static int kx022a_write_raw_get_fmt(struct iio_dev *idev,
> +				    struct iio_chan_spec const *chan,
> +				    long mask)
> +{
> +	switch (mask) {
> +	case IIO_CHAN_INFO_SCALE:
> +		return IIO_VAL_INT_PLUS_NANO;
> +	case IIO_CHAN_INFO_SAMP_FREQ:
> +		return IIO_VAL_INT_PLUS_MICRO;
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
>  static int kx022a_write_raw(struct iio_dev *idev,
>  			    struct iio_chan_spec const *chan,
>  			    int val, int val2, long mask)
> @@ -510,7 +524,7 @@ static int kx022a_read_raw(struct iio_dev *idev,
>  
>  		kx022a_reg2scale(regval, val, val2);
>  
> -		return IIO_VAL_INT_PLUS_MICRO;
> +		return IIO_VAL_INT_PLUS_NANO;
>  	}
>  
>  	return -EINVAL;
> @@ -712,6 +726,7 @@ static int kx022a_fifo_flush(struct iio_dev *idev, unsigned int samples)
>  static const struct iio_info kx022a_info = {
>  	.read_raw = &kx022a_read_raw,
>  	.write_raw = &kx022a_write_raw,
> +	.write_raw_get_fmt = &kx022a_write_raw_get_fmt,
>  	.read_avail = &kx022a_read_avail,
>  
>  	.validate_trigger	= iio_validate_own_trigger,