diff mbox series

[v4,05/10] iio: afe: rescale: add INT_PLUS_{MICRO,NANO} support

Message ID 20210706160942.3181474-6-liambeguin@gmail.com (mailing list archive)
State Changes Requested
Delegated to: Jonathan Cameron
Headers show
Series iio: afe: add temperature rescaling support | expand

Commit Message

Liam Beguin July 6, 2021, 4:09 p.m. UTC 
From: Liam Beguin <lvb@xiphos.com>

Add IIO_VAL_INT_PLUS_{NANO,MICRO} scaling support.
Scale the integer part and the decimal parts individually and keep the
original scaling type.

Signed-off-by: Liam Beguin <lvb@xiphos.com>
---
 drivers/iio/afe/iio-rescale.c | 8 ++++++++
 1 file changed, 8 insertions(+)

Comments

Peter Rosin July 9, 2021, 4:29 p.m. UTC | #1 
On 2021-07-06 18:09, Liam Beguin wrote:
> From: Liam Beguin <lvb@xiphos.com>
> 
> Add IIO_VAL_INT_PLUS_{NANO,MICRO} scaling support.
> Scale the integer part and the decimal parts individually and keep the
> original scaling type.
> 
> Signed-off-by: Liam Beguin <lvb@xiphos.com>
> ---
>  drivers/iio/afe/iio-rescale.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
> index ba3bdcc69b16..1d0e24145d87 100644
> --- a/drivers/iio/afe/iio-rescale.c
> +++ b/drivers/iio/afe/iio-rescale.c
> @@ -89,7 +89,15 @@ static int rescale_read_raw(struct iio_dev *indio_dev,
>  			do_div(tmp, 1000000000LL);
>  			*val = tmp;
>  			return ret;
> +		case IIO_VAL_INT_PLUS_NANO:
> +		case IIO_VAL_INT_PLUS_MICRO:
> +			tmp = (s64)*val * rescale->numerator;
> +			*val = div_s64(tmp, rescale->denominator);
> +			tmp = (s64)*val2 * rescale->numerator;
> +			*val2 = div_s64(tmp, rescale->denominator);

Hi!

You are losing precision, and you are not mormalising after the calculation.
I think it's better to not even attempt this given that the results can be
really poor.

Cheers,
Peter

> +			return ret;
>  		default:
> +			dev_err(&indio_dev->dev, "unsupported type %d\n", ret);
>  			return -EOPNOTSUPP;
>  		}
>  	default:
>
Liam Beguin July 9, 2021, 7:30 p.m. UTC | #2 
On Fri Jul 9, 2021 at 12:29 PM EDT, Peter Rosin wrote:
>
>
> On 2021-07-06 18:09, Liam Beguin wrote:
> > From: Liam Beguin <lvb@xiphos.com>
> > 
> > Add IIO_VAL_INT_PLUS_{NANO,MICRO} scaling support.
> > Scale the integer part and the decimal parts individually and keep the
> > original scaling type.
> > 
> > Signed-off-by: Liam Beguin <lvb@xiphos.com>
> > ---
> >  drivers/iio/afe/iio-rescale.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
> > index ba3bdcc69b16..1d0e24145d87 100644
> > --- a/drivers/iio/afe/iio-rescale.c
> > +++ b/drivers/iio/afe/iio-rescale.c
> > @@ -89,7 +89,15 @@ static int rescale_read_raw(struct iio_dev *indio_dev,
> >  			do_div(tmp, 1000000000LL);
> >  			*val = tmp;
> >  			return ret;
> > +		case IIO_VAL_INT_PLUS_NANO:
> > +		case IIO_VAL_INT_PLUS_MICRO:
> > +			tmp = (s64)*val * rescale->numerator;
> > +			*val = div_s64(tmp, rescale->denominator);
> > +			tmp = (s64)*val2 * rescale->numerator;
> > +			*val2 = div_s64(tmp, rescale->denominator);
>

Hi Peter,

> Hi!
>
> You are losing precision, and you are not mormalising after the
> calculation.

Can you elaborate a little on what you mean here?

Do you mean that I should make sure that *val2, the PLUS_{NANO,MICRO}
part, doesn't contain an integer part? And if so transfer that part back
to *val?

> I think it's better to not even attempt this given that the results can
> be
> really poor.

Unfortunatelly, I'm kinda stuck with this as some of my ADC use these
types.

Thanks,
Liam

>
> Cheers,
> Peter
>
> > +			return ret;
> >  		default:
> > +			dev_err(&indio_dev->dev, "unsupported type %d\n", ret);
> >  			return -EOPNOTSUPP;
> >  		}
> >  	default:
> >
Peter Rosin July 10, 2021, 8:14 a.m. UTC | #3 
On 2021-07-09 21:30, Liam Beguin wrote:
> On Fri Jul 9, 2021 at 12:29 PM EDT, Peter Rosin wrote:
>>
>>
>> On 2021-07-06 18:09, Liam Beguin wrote:
>>> From: Liam Beguin <lvb@xiphos.com>
>>>
>>> Add IIO_VAL_INT_PLUS_{NANO,MICRO} scaling support.
>>> Scale the integer part and the decimal parts individually and keep the
>>> original scaling type.
>>>
>>> Signed-off-by: Liam Beguin <lvb@xiphos.com>
>>> ---
>>>  drivers/iio/afe/iio-rescale.c | 8 ++++++++
>>>  1 file changed, 8 insertions(+)
>>>
>>> diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
>>> index ba3bdcc69b16..1d0e24145d87 100644
>>> --- a/drivers/iio/afe/iio-rescale.c
>>> +++ b/drivers/iio/afe/iio-rescale.c
>>> @@ -89,7 +89,15 @@ static int rescale_read_raw(struct iio_dev *indio_dev,
>>>  			do_div(tmp, 1000000000LL);
>>>  			*val = tmp;
>>>  			return ret;
>>> +		case IIO_VAL_INT_PLUS_NANO:
>>> +		case IIO_VAL_INT_PLUS_MICRO:
>>> +			tmp = (s64)*val * rescale->numerator;
>>> +			*val = div_s64(tmp, rescale->denominator);
>>> +			tmp = (s64)*val2 * rescale->numerator;
>>> +			*val2 = div_s64(tmp, rescale->denominator);
>>
> 
> Hi Peter,
> 
>> Hi!
>>
>> You are losing precision, and you are not mormalising after the
>> calculation.
> 
> Can you elaborate a little on what you mean here?
> 
> Do you mean that I should make sure that *val2, the PLUS_{NANO,MICRO}
> part, doesn't contain an integer part? And if so transfer that part back
> to *val?

Yes. On 32-bit, you will easily wrap, especially for PLUS_NANO. You'd
only need a scale factor of 10 or so and a fractional part above .5 to
hit the roof (10 * 500000000 > 2^32).

But I also mean that you are losing precision when you are scaling
the integer part and the fractional part separately. That deserves
at least a comment, but ideally it should be handled correctly.

>> I think it's better to not even attempt this given that the results can
>> be
>> really poor.
> 
> Unfortunatelly, I'm kinda stuck with this as some of my ADC use these
> types.

Ok. Crap. :-)

Cheers,
Peter
Liam Beguin July 10, 2021, 5:45 p.m. UTC | #4 
On Sat Jul 10, 2021 at 4:14 AM EDT, Peter Rosin wrote:
>
>
> On 2021-07-09 21:30, Liam Beguin wrote:
> > On Fri Jul 9, 2021 at 12:29 PM EDT, Peter Rosin wrote:
> >>
> >>
> >> On 2021-07-06 18:09, Liam Beguin wrote:
> >>> From: Liam Beguin <lvb@xiphos.com>
> >>>
> >>> Add IIO_VAL_INT_PLUS_{NANO,MICRO} scaling support.
> >>> Scale the integer part and the decimal parts individually and keep the
> >>> original scaling type.
> >>>
> >>> Signed-off-by: Liam Beguin <lvb@xiphos.com>
> >>> ---
> >>>  drivers/iio/afe/iio-rescale.c | 8 ++++++++
> >>>  1 file changed, 8 insertions(+)
> >>>
> >>> diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
> >>> index ba3bdcc69b16..1d0e24145d87 100644
> >>> --- a/drivers/iio/afe/iio-rescale.c
> >>> +++ b/drivers/iio/afe/iio-rescale.c
> >>> @@ -89,7 +89,15 @@ static int rescale_read_raw(struct iio_dev *indio_dev,
> >>>  			do_div(tmp, 1000000000LL);
> >>>  			*val = tmp;
> >>>  			return ret;
> >>> +		case IIO_VAL_INT_PLUS_NANO:
> >>> +		case IIO_VAL_INT_PLUS_MICRO:
> >>> +			tmp = (s64)*val * rescale->numerator;
> >>> +			*val = div_s64(tmp, rescale->denominator);
> >>> +			tmp = (s64)*val2 * rescale->numerator;
> >>> +			*val2 = div_s64(tmp, rescale->denominator);
> >>
> > 
> > Hi Peter,
> > 
> >> Hi!
> >>
> >> You are losing precision, and you are not mormalising after the
> >> calculation.
> > 
> > Can you elaborate a little on what you mean here?
> > 
> > Do you mean that I should make sure that *val2, the PLUS_{NANO,MICRO}
> > part, doesn't contain an integer part? And if so transfer that part back
> > to *val?

Hi Peter,

>
> Yes. On 32-bit, you will easily wrap, especially for PLUS_NANO. You'd
> only need a scale factor of 10 or so and a fractional part above .5 to
> hit the roof (10 * 500000000 > 2^32).
>

Right, That makes sense!

> But I also mean that you are losing precision when you are scaling
> the integer part and the fractional part separately. That deserves
> at least a comment, but ideally it should be handled correctly.
>

Oh got it! Apologies, How did I miss that...

All things considered, it might make sense to also implement the
test case Jonathan mentioned [1]. I'll look into it.

[1] https://lore.kernel.org/linux-devicetree/20210704173639.622371bf@jic23-huawei/

> >> I think it's better to not even attempt this given that the results can
> >> be
> >> really poor.
> > 
> > Unfortunatelly, I'm kinda stuck with this as some of my ADC use these
> > types.
>
> Ok. Crap. :-)

Can't agree more :-)

Thanks,
Liam

>
> Cheers,
> Peter
diff mbox series

Patch

diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
index ba3bdcc69b16..1d0e24145d87 100644
--- a/drivers/iio/afe/iio-rescale.c
+++ b/drivers/iio/afe/iio-rescale.c
@@ -89,7 +89,15 @@  static int rescale_read_raw(struct iio_dev *indio_dev,
 			do_div(tmp, 1000000000LL);
 			*val = tmp;
 			return ret;
+		case IIO_VAL_INT_PLUS_NANO:
+		case IIO_VAL_INT_PLUS_MICRO:
+			tmp = (s64)*val * rescale->numerator;
+			*val = div_s64(tmp, rescale->denominator);
+			tmp = (s64)*val2 * rescale->numerator;
+			*val2 = div_s64(tmp, rescale->denominator);
+			return ret;
 		default:
+			dev_err(&indio_dev->dev, "unsupported type %d\n", ret);
 			return -EOPNOTSUPP;
 		}
 	default: