Re: [PATCH v2 07/13] staging: iio: ad2s1200: Improve readability with be16_to_cpup

[David Julian Veenstra]

On 21, April 2018 18:55, Jonathan Cameron wrote:

> On Fri, 20 Apr 2018 21:30:32 +0200
> David Veenstra  wrote:
>
>> The manual states that the data is contained in the upper 12 bits
>> of the 16 bits read by spi. The code that extracts these 12 bits
>> is correct for both be and le machines, but this is not clear
>> from a first glance.
>> 
>> To improve readability the relevant expressions are replaced
>> with equivalent expressions that use be16_to_cpup.
>> 
>> Signed-off-by: David Veenstra 
>> ---
>>  drivers/staging/iio/resolver/ad2s1200.c | 9 -
>>  1 file changed, 4 insertions(+), 5 deletions(-)
>> 
>> diff --git a/drivers/staging/iio/resolver/ad2s1200.c 
>> b/drivers/staging/iio/resolver/ad2s1200.c
>> index 0a5fc9917e32..11ed9c7332e6 100644
>> --- a/drivers/staging/iio/resolver/ad2s1200.c
>> +++ b/drivers/staging/iio/resolver/ad2s1200.c
>> @@ -57,7 +57,7 @@ static int ad2s1200_read_raw(struct iio_dev *indio_dev,
>>  {
>>  struct ad2s1200_state *st = iio_priv(indio_dev);
>>  int ret = 0;
>> -s16 vel;
>> +u16 vel;
>>  
>>  mutex_lock(>lock);
>>  gpio_set_value(st->sample, 0);
>> @@ -73,14 +73,13 @@ static int ad2s1200_read_raw(struct iio_dev *indio_dev,
>>  return ret;
>>  }
>>  
>> +vel = be16_to_cpup((__be16 *)st->rx);
> Well it isn't vel (velocity) in one case so now the name is misleading.
>
> Also that type cast suggests a fairly obvious cleanup associated with this 
> one.
> Why not make st->rx a __be16 in the first pace avoiding the need to cast at 
> all?
>
> Then you could just have *val = be16_to_cpu(st->rx) >> 4 and similar.

Agreed on naming of vel, and type of st-rx. I'll change this for v3.

Best regards,
David Veenstra

>
>>  switch (chan->type) {
>>  case IIO_ANGL:
>> -*val = (((u16)(st->rx[0])) << 4) | ((st->rx[1] & 0xF0) >> 4);
>> +*val = vel >> 4;
>>  break;
>>  case IIO_ANGL_VEL:
>> -vel = (((s16)(st->rx[0])) << 4) | ((st->rx[1] & 0xF0) >> 4);
>> -vel = sign_extend32(vel, 11);
>> -*val = vel;
>> +*val = sign_extend32((s16)vel >> 4, 11);
> If you were to use an intermediate that was s16 then the sign extend would
> be automatic.  Perhaps it is clear to do it like this though.. 
> Up to you.
>
>>  break;
>>  default:
>>  mutex_unlock(>lock);

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Re: [PATCH v2 07/13] staging: iio: ad2s1200: Improve readability with be16_to_cpup

[Jonathan Cameron]

On Fri, 20 Apr 2018 21:30:32 +0200
David Veenstra  wrote:

> The manual states that the data is contained in the upper 12 bits
> of the 16 bits read by spi. The code that extracts these 12 bits
> is correct for both be and le machines, but this is not clear
> from a first glance.
> 
> To improve readability the relevant expressions are replaced
> with equivalent expressions that use be16_to_cpup.
> 
> Signed-off-by: David Veenstra 
> ---
>  drivers/staging/iio/resolver/ad2s1200.c | 9 -
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/staging/iio/resolver/ad2s1200.c 
> b/drivers/staging/iio/resolver/ad2s1200.c
> index 0a5fc9917e32..11ed9c7332e6 100644
> --- a/drivers/staging/iio/resolver/ad2s1200.c
> +++ b/drivers/staging/iio/resolver/ad2s1200.c
> @@ -57,7 +57,7 @@ static int ad2s1200_read_raw(struct iio_dev *indio_dev,
>  {
>   struct ad2s1200_state *st = iio_priv(indio_dev);
>   int ret = 0;
> - s16 vel;
> + u16 vel;
>  
>   mutex_lock(>lock);
>   gpio_set_value(st->sample, 0);
> @@ -73,14 +73,13 @@ static int ad2s1200_read_raw(struct iio_dev *indio_dev,
>   return ret;
>   }
>  
> + vel = be16_to_cpup((__be16 *)st->rx);
Well it isn't vel (velocity) in one case so now the name is misleading.

Also that type cast suggests a fairly obvious cleanup associated with this one.
Why not make st->rx a __be16 in the first pace avoiding the need to cast at all?

Then you could just have *val = be16_to_cpu(st->rx) >> 4 and similar.

>   switch (chan->type) {
>   case IIO_ANGL:
> - *val = (((u16)(st->rx[0])) << 4) | ((st->rx[1] & 0xF0) >> 4);
> + *val = vel >> 4;
>   break;
>   case IIO_ANGL_VEL:
> - vel = (((s16)(st->rx[0])) << 4) | ((st->rx[1] & 0xF0) >> 4);
> - vel = sign_extend32(vel, 11);
> - *val = vel;
> + *val = sign_extend32((s16)vel >> 4, 11);
If you were to use an intermediate that was s16 then the sign extend would
be automatic.  Perhaps it is clear to do it like this though.. 
Up to you.

>   break;
>   default:
>   mutex_unlock(>lock);

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