linux-kernel - Re: [PATCH 1/3] iio: core: add IIO_VAL_INT

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Date:   Wed, 12 Apr 2023 21:32:08 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Matti Vaittinen <mazziesaccount@...il.com>
Cc:     Matti Vaittinen <matti.vaittinen@...rohmeurope.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] iio: core: add IIO_VAL_INT_MICRO

On Wed, 12 Apr 2023 15:27:14 +0300
Matti Vaittinen <mazziesaccount@...il.com> wrote:

> There are a few cases like light sensor integration times, where values
> returned from *_available() and read_raw() are smaller than 1 and often
> in the units of micro. (Like micro second scale integration times,
> always smaller than 1 second). Currently those are often handled using
> IIO_VAL_INT_PLUS_MICRO, which requires drivers to initialize the integer
> part to zero. Furthermore, using IIO_VAL_INT_PLUS_MICRO in iio lists
> requires one to always allocate the 'dummy' integer part too.
> 
> Introduce IIO_VAL_INT_MICRO which allows omitting the always zero integer.
> 
> Signed-off-by: Matti Vaittinen <mazziesaccount@...il.com>
Hi Matti,

I'm not keen on adding yet another case just to avoid having to
have the integer part for IIO_VAL_INT_PLUS_MICRO.
Seems like the wrong trade off of maintainability vs ease of use.

Jonathan

> ---
>  drivers/iio/industrialio-core.c | 4 ++++
>  include/linux/iio/types.h       | 1 +
>  2 files changed, 5 insertions(+)
> 
> diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> index c117f50d0cf3..c5ae965e9961 100644
> --- a/drivers/iio/industrialio-core.c
> +++ b/drivers/iio/industrialio-core.c
> @@ -628,6 +628,8 @@ static ssize_t __iio_format_value(char *buf, size_t offset, unsigned int type,
>  	switch (type) {
>  	case IIO_VAL_INT:
>  		return sysfs_emit_at(buf, offset, "%d", vals[0]);
> +	case IIO_VAL_INT_MICRO:
> +		return sysfs_emit_at(buf, offset, "0.%06u", vals[0]);
>  	case IIO_VAL_INT_PLUS_MICRO_DB:
>  		scale_db = true;
>  		fallthrough;
> @@ -758,6 +760,7 @@ static ssize_t iio_format_list(char *buf, const int *vals, int type, int length,
>  
>  	switch (type) {
>  	case IIO_VAL_INT:
> +	case IIO_VAL_INT_MICRO:
>  		stride = 1;
>  		break;
>  	default:
> @@ -952,6 +955,7 @@ static ssize_t iio_write_channel_info(struct device *dev,
>  		case IIO_VAL_INT_PLUS_MICRO_DB:
>  			scale_db = true;
>  			fallthrough;
> +		case IIO_VAL_INT_MICRO:
>  		case IIO_VAL_INT_PLUS_MICRO:
>  			fract_mult = 100000;
>  			break;
> diff --git a/include/linux/iio/types.h b/include/linux/iio/types.h
> index 82faa98c719a..b4e316172c7f 100644
> --- a/include/linux/iio/types.h
> +++ b/include/linux/iio/types.h
> @@ -30,6 +30,7 @@ enum iio_event_info {
>  #define IIO_VAL_FRACTIONAL 10
>  #define IIO_VAL_FRACTIONAL_LOG2 11
>  #define IIO_VAL_CHAR 12
> +#define IIO_VAL_INT_MICRO 13 /* val is micro <units>. Integer part is 0 */
>  
>  enum iio_available_type {
>  	IIO_AVAIL_LIST,