[PATCH] iio: adc: ad7192: Change "shorted" channels to differential

[PATCH] iio: adc: ad7192: Change "shorted" channels to differential

[Paul Cercueil]

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")
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Co-developed-by: Alisa Roman <alisa.roman@analog.com>
Signed-off-by: Alisa Roman <alisa.roman@analog.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),
-- 
2.39.2

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

[Paul Cercueil]

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@vger.kernel.org

D'oh.

-Paul

> Signed-off-by: Paul Cercueil <paul@crapouillou.net>
> Co-developed-by: Alisa Roman <alisa.roman@analog.com>
> Signed-off-by: Alisa Roman <alisa.roman@analog.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),

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

[Nuno Sá]

On Thu, 2023-03-30 at 12:21 +0200, Paul Cercueil wrote:
> 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")
> Signed-off-by: Paul Cercueil <paul@crapouillou.net>
> Co-developed-by: Alisa Roman <alisa.roman@analog.com>
> Signed-off-by: Alisa Roman <alisa.roman@analog.com>
> ---

Reviewed-by: Nuno Sa <nuno.sa@analog.com>

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

[Jonathan Cameron]

On Thu, 30 Mar 2023 12:21:00 +0200
Paul Cercueil <paul@crapouillou.net> wrote:

> 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")
> Signed-off-by: Paul Cercueil <paul@crapouillou.net>
> Co-developed-by: Alisa Roman <alisa.roman@analog.com>
> Signed-off-by: Alisa Roman <alisa.roman@analog.com>

+CC Fabrizio who has a fix series under review for the same driver.

I'm going to let this one sit on the list for a little while.
It is a breaking ABI change (that hopefully no one will notice - given
the first fix from Fabrizio shows the driver crashes on probe currently we
should be safe on that).

Arguably just changing the index would also have been an ABI change, but
that would have gotten past any code that didn't take much notice of the
channel index whereas this won't.

Anyhow, will give it a little while for comments then pick this up
on top of Fabrizio's fixes series.  Give me a poke in 2-3 weeks if I
seem to have lost it.

Jonathan


> ---
>  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),

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

[Fabrizio Lamarque]

On Sat, Apr 1, 2023 at 4:27 PM Jonathan Cameron <jic23@kernel.org> wrote:
>
> On Thu, 30 Mar 2023 12:21:00 +0200
> Paul Cercueil <paul@crapouillou.net> wrote:
>
> > 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")
> > Signed-off-by: Paul Cercueil <paul@crapouillou.net>
> > Co-developed-by: Alisa Roman <alisa.roman@analog.com>
> > Signed-off-by: Alisa Roman <alisa.roman@analog.com>
>
> +CC Fabrizio who has a fix series under review for the same driver.
>
> I'm going to let this one sit on the list for a little while.
> It is a breaking ABI change (that hopefully no one will notice - given
> the first fix from Fabrizio shows the driver crashes on probe currently we
> should be safe on that).
>
> Arguably just changing the index would also have been an ABI change, but
> that would have gotten past any code that didn't take much notice of the
> channel index whereas this won't.
>
> Anyhow, will give it a little while for comments then pick this up
> on top of Fabrizio's fixes series.  Give me a poke in 2-3 weeks if I
> seem to have lost it.

The bug report in libiio related to this patch was from the company I work for.
I guess this confirms there are few actual users of the driver (at least
of its later revisions).

I see a somewhat limited usage of the "input2 vs input2" configuration,
it was just causing a libiio initialization issue, without impacting
sysfs operation.
The breaking ABI change would impact only users of this channel
relying on sysfs without libiio.

I tested this patch and I confirm it solves the issue with libiio.

Fabrizio

>
> Jonathan
>
>
> > ---
> >  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),
>

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

[Paul Cercueil]

Hi Jonathan,

Le samedi 01 avril 2023 à 15:42 +0100, Jonathan Cameron a écrit :
> On Thu, 30 Mar 2023 12:21:00 +0200
> Paul Cercueil <paul@crapouillou.net> wrote:
> 
> > 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")
> > Signed-off-by: Paul Cercueil <paul@crapouillou.net>
> > Co-developed-by: Alisa Roman <alisa.roman@analog.com>
> > Signed-off-by: Alisa Roman <alisa.roman@analog.com>
> 
> +CC Fabrizio who has a fix series under review for the same driver.
> 
> I'm going to let this one sit on the list for a little while.
> It is a breaking ABI change (that hopefully no one will notice -
> given
> the first fix from Fabrizio shows the driver crashes on probe
> currently we
> should be safe on that).
> 
> Arguably just changing the index would also have been an ABI change,
> but
> that would have gotten past any code that didn't take much notice of
> the
> channel index whereas this won't.
> 
> Anyhow, will give it a little while for comments then pick this up
> on top of Fabrizio's fixes series.  Give me a poke in 2-3 weeks if I
> seem to have lost it.

Friendly ping :)

Cheers,
-Paul

> 
> Jonathan
> 
> 
> > ---
> >  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),
> 

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

[Jonathan Cameron]

On Tue, 25 Apr 2023 11:07:11 +0200
Paul Cercueil <paul@crapouillou.net> wrote:

> Hi Jonathan,
> 
> Le samedi 01 avril 2023 à 15:42 +0100, Jonathan Cameron a écrit :
> > On Thu, 30 Mar 2023 12:21:00 +0200
> > Paul Cercueil <paul@crapouillou.net> wrote:
> >   
> > > 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")
> > > Signed-off-by: Paul Cercueil <paul@crapouillou.net>
> > > Co-developed-by: Alisa Roman <alisa.roman@analog.com>
> > > Signed-off-by: Alisa Roman <alisa.roman@analog.com>  
> > 
> > +CC Fabrizio who has a fix series under review for the same driver.
> > 
> > I'm going to let this one sit on the list for a little while.
> > It is a breaking ABI change (that hopefully no one will notice -
> > given
> > the first fix from Fabrizio shows the driver crashes on probe
> > currently we
> > should be safe on that).
> > 
> > Arguably just changing the index would also have been an ABI change,
> > but
> > that would have gotten past any code that didn't take much notice of
> > the
> > channel index whereas this won't.
> > 
> > Anyhow, will give it a little while for comments then pick this up
> > on top of Fabrizio's fixes series.  Give me a poke in 2-3 weeks if I
> > seem to have lost it.  
> 
> Friendly ping :)

Wise move :)

Applied to the fixes-togreg branch of iio.git and marked for stable.

Thanks,

Jonathan

> 
> Cheers,
> -Paul
> 
> > 
> > Jonathan
> > 
> >   
> > > ---
> > >  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),  
> >   
>