linux-kernel - Re: [PATCH v2 06/19] staging: iio: resolver: ad2s1210: always use 16-bit value for raw read

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Date:   Sun, 24 Sep 2023 18:31:36 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     David Lechner <dlechner@...libre.com>
Cc:     linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Michael Hennerich <Michael.Hennerich@...log.com>,
        Nuno Sá <nuno.sa@...log.com>,
        Axel Haslam <ahaslam@...libre.com>,
        Philip Molloy <pmolloy@...libre.com>
Subject: Re: [PATCH v2 06/19] staging: iio: resolver: ad2s1210: always use
 16-bit value for raw read

On Thu, 21 Sep 2023 09:43:47 -0500
David Lechner <dlechner@...libre.com> wrote:

> This removes the special handling for resolutions lower than 16 bits.
> This will allow us to use a fixed scale independent of the resolution.
> 
> Also, for the record, according to the datasheet, the logic for the
> special handling based on hysteresis that was removed was incorrect.
> 
> Signed-off-by: David Lechner <dlechner@...libre.com>
This looks fine to me, but a potential improvement would be to just
use a __be16 element in st in the first place have the type explicitly
marked all the way through.

Jonathan


> ---
>  drivers/staging/iio/resolver/ad2s1210.c | 16 ++--------------
>  1 file changed, 2 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/staging/iio/resolver/ad2s1210.c b/drivers/staging/iio/resolver/ad2s1210.c
> index 9c7f76114360..985b8fecd65a 100644
> --- a/drivers/staging/iio/resolver/ad2s1210.c
> +++ b/drivers/staging/iio/resolver/ad2s1210.c
> @@ -465,10 +465,7 @@ static int ad2s1210_read_raw(struct iio_dev *indio_dev,
>  			     long m)
>  {
>  	struct ad2s1210_state *st = iio_priv(indio_dev);
> -	u16 negative;
>  	int ret = 0;
> -	u16 pos;
> -	s16 vel;
>  
>  	mutex_lock(&st->lock);
>  	gpiod_set_value(st->gpios[AD2S1210_SAMPLE], 0);
> @@ -494,20 +491,11 @@ static int ad2s1210_read_raw(struct iio_dev *indio_dev,
>  
>  	switch (chan->type) {
>  	case IIO_ANGL:
> -		pos = be16_to_cpup((__be16 *)st->rx);
> -		if (st->hysteresis)
> -			pos >>= 16 - st->resolution;
> -		*val = pos;
> +		*val = be16_to_cpup((__be16 *)st->rx);

Could be made more obvious still by adding as suitable __be16 to read into in the
first place.

>  		ret = IIO_VAL_INT;
>  		break;
>  	case IIO_ANGL_VEL:
> -		vel = be16_to_cpup((__be16 *)st->rx);
> -		vel >>= 16 - st->resolution;
> -		if (vel & 0x8000) {
> -			negative = (0xffff >> st->resolution) << st->resolution;
> -			vel |= negative;
> -		}
> -		*val = vel;
> +		*val = (s16)be16_to_cpup((__be16 *)st->rx);
>  		ret = IIO_VAL_INT;
>  		break;
>  	default: