Re: [PATCH 10/11] staging: iio: ad2s1200: Replace angle channel with inclination channel

From: Jonathan Cameron <Jonathan.Cameron@huawei.com>
To: David Veenstra <davidjulianveenstra@gmail.com>
Cc: <lars@metafoo.de>, <jic23@kernel.org>,
	<Michael.Hennerich@analog.com>, <knaack.h@gmx.de>,
	<linux-iio@vger.kernel.org>, <devel@driverdev.osuosl.org>
Subject: Re: [PATCH 10/11] staging: iio: ad2s1200: Replace angle channel with inclination channel
Date: Fri, 23 Mar 2018 13:27:48 +0000	[thread overview]
Message-ID: <20180323142748.00005fec@huawei.com> (raw)
In-Reply-To: <73912d42bd2718325313ec792f8402a20f47405c.1521379685.git.davidjulianveenstra@gmail.com>

On Sun, 18 Mar 2018 14:37:04 +0100
David Veenstra <davidjulianveenstra@gmail.com> wrote:

> The angle channel is not defined in sysfs iio ABI. So it is replaced
> with an inclination channel, because it is defined in the ABI, and has the
> semantics of an angle.
> 
> In addition, a fractional scaling factor of 360 / (2^12 -1) is added,
> to scale the 12-bits angular position to degrees, conform the ABI.
> 
> Signed-off-by: David Veenstra <davidjulianveenstra@gmail.com>
No, please do not blugeon a device into the existing documented ABI.

A resolver does not measure something that can be remotely
sensibly mapped to inclination.  Inclination is relative to 'down'.
A resolver doesn't care about down.

Add an angle type to the ABI docs. It simply hasn't been documented
before because there were no drivers outside staging that use it.

Jonathan

> ---
>  drivers/staging/iio/resolver/ad2s1200.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/staging/iio/resolver/ad2s1200.c b/drivers/staging/iio/resolver/ad2s1200.c
> index 4b97a106012c..937676bcc0d4 100644
> --- a/drivers/staging/iio/resolver/ad2s1200.c
> +++ b/drivers/staging/iio/resolver/ad2s1200.c
> @@ -64,6 +64,10 @@ static int ad2s1200_read_raw(struct iio_dev *indio_dev,
>  	switch (m) {
>  	case IIO_CHAN_INFO_SCALE:
>  		switch (chan->type) {
> +		case IIO_INCLI:
> +			*val = 360;
> +			*val2 = 0xFFF;
> +			return IIO_VAL_FRACTIONAL;
>  		case IIO_ANGL_VEL:
>  			/*
>  			 * 2 * Pi is almost equal to
> @@ -91,7 +95,7 @@ static int ad2s1200_read_raw(struct iio_dev *indio_dev,
>  		/* delay (6 * AD2S1200_TSCLK + 20) nano seconds */
>  		udelay(1);
>  		gpiod_set_value(st->sample, 1);
> -		gpiod_set_value(st->rdvel, !!(chan->type == IIO_ANGL));
> +		gpiod_set_value(st->rdvel, !!(chan->type == IIO_INCLI));
>  
>  		ret = spi_read(st->sdev, st->rx, 2);
>  		if (ret < 0) {
> @@ -101,7 +105,7 @@ static int ad2s1200_read_raw(struct iio_dev *indio_dev,
>  
>  		vel = be16_to_cpup((__be16 *)st->rx);
>  		switch (chan->type) {
> -		case IIO_ANGL:
> +		case IIO_INCLI:
>  			*val = vel >> 4;
>  			ret = IIO_VAL_INT;
>  			break;
> @@ -128,10 +132,11 @@ static int ad2s1200_read_raw(struct iio_dev *indio_dev,
>  
>  static const struct iio_chan_spec ad2s1200_channels[] = {
>  	{
> -		.type = IIO_ANGL,
> +		.type = IIO_INCLI,
>  		.indexed = 1,
>  		.channel = 0,
>  		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
> +		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),
>  	}, {
>  		.type = IIO_ANGL_VEL,
>  		.indexed = 1,