linux-kernel - Re: [PATCH v3 07/27] staging: iio: resolver: ad2s1210: always use 16-bit value for raw read

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Date:   Sat, 30 Sep 2023 15:41:15 +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,
        David Lechner <david@...hnology.com>,
        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>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 07/27] staging: iio: resolver: ad2s1210: always use
 16-bit value for raw read

On Fri, 29 Sep 2023 12:23:12 -0500
David Lechner <dlechner@...libre.com> wrote:

> From: David Lechner <david@...hnology.com>
> 
> From: David Lechner <dlechner@...libre.com>
> 
> This removes the special handling for resolutions lower than 16 bits.
> This will allow us to use a fixed scale independent of the resolution.
> 
> A new sample field is added to store the raw data instead of reusing
> the config mode rx buffer so that we don't have to do a cast or worry
> about unaligned access.
> 
> 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>
LGTM

Applied.

Thanks,

Jonathan

> ---
> 
> v3 changes:
> * Added __be16 sample field to state struct and use instead of rx buffer.
> 
>  drivers/staging/iio/resolver/ad2s1210.c | 24 ++++++++----------------
>  1 file changed, 8 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/staging/iio/resolver/ad2s1210.c b/drivers/staging/iio/resolver/ad2s1210.c
> index 832f86bf15e5..f9774dff2df4 100644
> --- a/drivers/staging/iio/resolver/ad2s1210.c
> +++ b/drivers/staging/iio/resolver/ad2s1210.c
> @@ -95,7 +95,11 @@ struct ad2s1210_state {
>  	bool hysteresis;
>  	u8 resolution;
>  	enum ad2s1210_mode mode;
> -	u8 rx[2] __aligned(IIO_DMA_MINALIGN);
> +	/** For reading raw sample value via SPI. */
> +	__be16 sample __aligned(IIO_DMA_MINALIGN);
> +	/** SPI transmit buffer. */
> +	u8 rx[2];
> +	/** SPI receive buffer. */
>  	u8 tx[2];
>  };
>  
> @@ -464,10 +468,7 @@ 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);
> @@ -487,26 +488,17 @@ static int ad2s1210_read_raw(struct iio_dev *indio_dev,
>  	}
>  	if (ret < 0)
>  		goto error_ret;
> -	ret = spi_read(st->sdev, st->rx, 2);
> +	ret = spi_read(st->sdev, &st->sample, 2);
>  	if (ret < 0)
>  		goto error_ret;
>  
>  	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_cpu(st->sample);
>  		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_cpu(st->sample);
>  		ret = IIO_VAL_INT;
>  		break;
>  	default:
>