linux-kernel - Re: [PATCH 2/3] staging: iio: cdc: ad7746: use dt bindings to set the EXCx pins output

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Date:   Sat, 10 Apr 2021 19:15:39 +0300
From:   Alexandru Ardelean <ardeleanalex@...il.com>
To:     Lucas Stankus <lucas.p.stankus@...il.com>
Cc:     Lars-Peter Clausen <lars@...afoo.de>,
        "Hennerich, Michael" <Michael.Hennerich@...log.com>,
        Jonathan Cameron <jic23@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-iio <linux-iio@...r.kernel.org>,
        linux-staging@...ts.linux.dev, LKML <linux-kernel@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>
Subject: Re: [PATCH 2/3] staging: iio: cdc: ad7746: use dt bindings to set the
 EXCx pins output

On Sat, Apr 10, 2021 at 7:12 PM Alexandru Ardelean
<ardeleanalex@...il.com> wrote:
>
> On Fri, Apr 9, 2021 at 9:51 PM Lucas Stankus <lucas.p.stankus@...il.com> wrote:
> >
> > Ditch platform_data fields in favor of device tree properties for
> > configuring EXCA and EXCB output.
> > This also removes the fields from the platform_data struct, since they're
> > not used anymore.
> >
> > Signed-off-by: Lucas Stankus <lucas.p.stankus@...il.com>
> > ---
> >  drivers/staging/iio/cdc/ad7746.c | 33 +++++++++++++++++---------------
> >  drivers/staging/iio/cdc/ad7746.h |  4 ----
> >  2 files changed, 18 insertions(+), 19 deletions(-)
> >
> > diff --git a/drivers/staging/iio/cdc/ad7746.c b/drivers/staging/iio/cdc/ad7746.c
> > index dfd71e99e872..63041b164dbe 100644
> > --- a/drivers/staging/iio/cdc/ad7746.c
> > +++ b/drivers/staging/iio/cdc/ad7746.c
> > @@ -677,8 +677,10 @@ static int ad7746_probe(struct i2c_client *client,
> >                         const struct i2c_device_id *id)
> >  {
> >         struct ad7746_platform_data *pdata = client->dev.platform_data;
> > +       struct device_node *np = client->dev.of_node;
> >         struct ad7746_chip_info *chip;
> >         struct iio_dev *indio_dev;
> > +       unsigned int exca_en, excb_en;
> >         unsigned char regval = 0;
> >         int ret = 0;
> >
> > @@ -703,26 +705,27 @@ static int ad7746_probe(struct i2c_client *client,
> >         indio_dev->num_channels = ARRAY_SIZE(ad7746_channels);
> >         indio_dev->modes = INDIO_DIRECT_MODE;
> >
>
> [1]
>
> > -       if (pdata) {
> > -               if (pdata->exca_en) {
> > -                       if (pdata->exca_inv_en)
> > -                               regval |= AD7746_EXCSETUP_NEXCA;
> > -                       else
> > -                               regval |= AD7746_EXCSETUP_EXCA;
> > -               }
> > +       ret = of_property_read_u32(np, "adi,exca-output", &exca_en);
>
> maybe a better idea would be to use:
>
> device_property_read_u32(dev, .... )
> where:
> dev = client->dev.;
>
> this would make the driver a bit more friendly with both OF and ACPI
>
> > +       if (!ret && exca_en) {
> > +               if (exca_en == 1)
> > +                       regval |= AD7746_EXCSETUP_EXCA;
> > +               else
> > +                       regval |= AD7746_EXCSETUP_NEXCA;
> > +       }
> >
> > -               if (pdata->excb_en) {
> > -                       if (pdata->excb_inv_en)
> > -                               regval |= AD7746_EXCSETUP_NEXCB;
> > -                       else
> > -                               regval |= AD7746_EXCSETUP_EXCB;
> > -               }
> > +       ret = of_property_read_u32(np, "adi,excb-output", &excb_en);
> > +       if (!ret && excb_en) {
> > +               if (excb_en == 1)
> > +                       regval |= AD7746_EXCSETUP_EXCB;
> > +               else
> > +                       regval |= AD7746_EXCSETUP_NEXCB;
> > +       }
> >
> > +       if (pdata) {
> >                 regval |= AD7746_EXCSETUP_EXCLVL(pdata->exclvl);
> >         } else {
> >                 dev_warn(&client->dev, "No platform data? using default\n");
> > -               regval = AD7746_EXCSETUP_EXCA | AD7746_EXCSETUP_EXCB |
> > -                       AD7746_EXCSETUP_EXCLVL(3);
>
> This logic is problematic now.
> Because no matter what you're setting in the DT, it always gets
> overridden here because there is no platform data.
>
> Maybe a better idea is to do something like:
> if (!pdata)
>      regval = AD7746_EXCSETUP_EXCLVL(3);
>
> but this should be placed somewhere around [1]

[ i can see that this logic will get corrected in the next patch]
to add here a bit: the idea of a patch is that it should try to not
introduce any [even temporary] breakage, even when it's in a series;
if a driver was already broken, then it should get fixed via it's own patch;
but no patch should introduce any breakages [if possible]

>
>
> > +               regval = AD7746_EXCSETUP_EXCLVL(3);
> >         }
> >
> >         ret = i2c_smbus_write_byte_data(chip->client,
> > diff --git a/drivers/staging/iio/cdc/ad7746.h b/drivers/staging/iio/cdc/ad7746.h
> > index 8bdbd732dbbd..6cae4ecf779e 100644
> > --- a/drivers/staging/iio/cdc/ad7746.h
> > +++ b/drivers/staging/iio/cdc/ad7746.h
> > @@ -19,10 +19,6 @@
> >
> >  struct ad7746_platform_data {
> >         unsigned char exclvl;   /*Excitation Voltage Level */
> > -       bool exca_en;           /* enables EXCA pin as the excitation output */
> > -       bool exca_inv_en;       /* enables /EXCA pin as the excitation output */
> > -       bool excb_en;           /* enables EXCB pin as the excitation output */
> > -       bool excb_inv_en;       /* enables /EXCB pin as the excitation output */
> >  };
> >
> >  #endif /* IIO_CDC_AD7746_H_ */
> > --
> > 2.31.1
> >