linux-kernel - Re: [PATCH] iio: adc: ad7192: Change "shorted" channels to differential

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Date:   Thu, 30 Mar 2023 12:22:23 +0200
From:   Paul Cercueil <paul@...pouillou.net>
To:     Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Michael Hennerich <Michael.Hennerich@...log.com>
Cc:     linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
        Alisa Roman <alisa.roman@...log.com>
Subject: Re: [PATCH] iio: adc: ad7192: Change "shorted" channels to
 differential

Le jeudi 30 mars 2023 à 12:21 +0200, Paul Cercueil a écrit :
> The AD7192 provides a specific channel configuration where both
> negative
> and positive inputs are connected to AIN2. This was represented in
> the
> ad7192 driver as a IIO channel with .channel = 2 and .extended_name
> set
> to "shorted".
> 
> The problem with this approach, is that the driver provided two IIO
> channels with the identifier .channel = 2; one "shorted" and the
> other
> not. This goes against the IIO ABI, as a channel identifier should be
> unique.
> 
> Address this issue by changing "shorted" channels to being
> differential
> instead, with channel 2 vs. itself, as we're actually measuring AIN2
> vs.
> itself.
> 
> Note that the fix tag is for the commit that moved the driver out of
> staging. The bug existed before that, but backporting would become
> very
> complex further down and unlikely to happen.
> 
> Fixes: b581f748cce0 ("staging: iio: adc: ad7192: move out of
> staging")

Forgot to Cc: stable@...r.kernel.org

D'oh.

-Paul

> Signed-off-by: Paul Cercueil <paul@...pouillou.net>
> Co-developed-by: Alisa Roman <alisa.roman@...log.com>
> Signed-off-by: Alisa Roman <alisa.roman@...log.com>
> ---
>  drivers/iio/adc/ad7192.c | 8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/iio/adc/ad7192.c b/drivers/iio/adc/ad7192.c
> index 55a6ab591016..99bb604b78c8 100644
> --- a/drivers/iio/adc/ad7192.c
> +++ b/drivers/iio/adc/ad7192.c
> @@ -897,10 +897,6 @@ static const struct iio_info ad7195_info = {
>         __AD719x_CHANNEL(_si, _channel1, -1, _address, NULL,
> IIO_VOLTAGE, \
>                 BIT(IIO_CHAN_INFO_SCALE), ad7192_calibsys_ext_info)
>  
> -#define AD719x_SHORTED_CHANNEL(_si, _channel1, _address) \
> -       __AD719x_CHANNEL(_si, _channel1, -1, _address, "shorted",
> IIO_VOLTAGE, \
> -               BIT(IIO_CHAN_INFO_SCALE), ad7192_calibsys_ext_info)
> -
>  #define AD719x_TEMP_CHANNEL(_si, _address) \
>         __AD719x_CHANNEL(_si, 0, -1, _address, NULL, IIO_TEMP, 0,
> NULL)
>  
> @@ -908,7 +904,7 @@ static const struct iio_chan_spec
> ad7192_channels[] = {
>         AD719x_DIFF_CHANNEL(0, 1, 2, AD7192_CH_AIN1P_AIN2M),
>         AD719x_DIFF_CHANNEL(1, 3, 4, AD7192_CH_AIN3P_AIN4M),
>         AD719x_TEMP_CHANNEL(2, AD7192_CH_TEMP),
> -       AD719x_SHORTED_CHANNEL(3, 2, AD7192_CH_AIN2P_AIN2M),
> +       AD719x_DIFF_CHANNEL(3, 2, 2, AD7192_CH_AIN2P_AIN2M),
>         AD719x_CHANNEL(4, 1, AD7192_CH_AIN1),
>         AD719x_CHANNEL(5, 2, AD7192_CH_AIN2),
>         AD719x_CHANNEL(6, 3, AD7192_CH_AIN3),
> @@ -922,7 +918,7 @@ static const struct iio_chan_spec
> ad7193_channels[] = {
>         AD719x_DIFF_CHANNEL(2, 5, 6, AD7193_CH_AIN5P_AIN6M),
>         AD719x_DIFF_CHANNEL(3, 7, 8, AD7193_CH_AIN7P_AIN8M),
>         AD719x_TEMP_CHANNEL(4, AD7193_CH_TEMP),
> -       AD719x_SHORTED_CHANNEL(5, 2, AD7193_CH_AIN2P_AIN2M),
> +       AD719x_DIFF_CHANNEL(5, 2, 2, AD7193_CH_AIN2P_AIN2M),
>         AD719x_CHANNEL(6, 1, AD7193_CH_AIN1),
>         AD719x_CHANNEL(7, 2, AD7193_CH_AIN2),
>         AD719x_CHANNEL(8, 3, AD7193_CH_AIN3),