linux-kernel - Re: [PATCH] iio: adc: Revoke valid channel for error path

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Message-ID: <CAKUZ0zL88AyuRxzhoAv2iZO7N7qOMy1G3yKscqG3rQiiOS0gog@mail.gmail.com>
Date: Thu, 17 Apr 2025 08:53:00 -0400
From: Gabriel Shahrouzi <gshahrouzi@...il.com>
To: Nuno Sá <noname.nuno@...il.com>
Cc: gregkh@...uxfoundation.org, jic23@...nel.org, lars@...afoo.de, 
	linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-staging@...ts.linux.dev, Michael.Hennerich@...log.com, 
	sonic.zhang@...log.com, vapier@...too.org, skhan@...uxfoundation.org, 
	kernelmentees@...ts.linuxfoundation.org, stable@...r.kernel.org
Subject: Re: [PATCH] iio: adc: Revoke valid channel for error path

On Thu, Apr 17, 2025 at 6:06 AM Nuno Sá <noname.nuno@...il.com> wrote:
>
> On Tue, 2025-04-15 at 14:20 -0400, Gabriel Shahrouzi wrote:
> > According to the datasheet on page 9 under the channel selection table,
> > all devices (AD7816/7/8) are able to use the channel marked as 7. This
> > channel is used for diagnostic purposes by routing the internal 1.23V
> > bandgap source through the MUX to the input of the ADC.
> >
> > Replace checking for string equality with checking for the same chip ID
> > to reduce time complexity.
> >
> > Group invalid channels for all devices together because they are
> > processed the same way.
> >
> > Fixes: 7924425db04a ("staging: iio: adc: new driver for AD7816 devices")
> > Cc: stable@...r.kernel.org
> > Signed-off-by: Gabriel Shahrouzi <gshahrouzi@...il.com>
> > ---
> >  drivers/staging/iio/adc/ad7816.c | 15 +++++----------
> >  1 file changed, 5 insertions(+), 10 deletions(-)
> >
> > diff --git a/drivers/staging/iio/adc/ad7816.c
> > b/drivers/staging/iio/adc/ad7816.c
> > index 6c14d7bcdd675..d880fe0257697 100644
> > --- a/drivers/staging/iio/adc/ad7816.c
> > +++ b/drivers/staging/iio/adc/ad7816.c
> > @@ -186,17 +186,12 @@ static ssize_t ad7816_store_channel(struct device *dev,
> >       if (ret)
> >               return ret;
> >
> > -     if (data > AD7816_CS_MAX && data != AD7816_CS_MASK) {
> > -             dev_err(&chip->spi_dev->dev, "Invalid channel id %lu for
> > %s.\n",
> > -                     data, indio_dev->name);
> > -             return -EINVAL;
> > -     } else if (strcmp(indio_dev->name, "ad7818") == 0 && data > 1) {
> > -             dev_err(&chip->spi_dev->dev,
> > -                     "Invalid channel id %lu for ad7818.\n", data);
> > -             return -EINVAL;
> > -     } else if (strcmp(indio_dev->name, "ad7816") == 0 && data > 0) {
> > +     if (data != AD7816_CS_MASK &&
> > +         (data > AD7816_CS_MAX ||
> > +         (chip->id == ID_AD7818 && data > 1) ||
> > +         (chip->id == ID_AD7816 && data > 0))) {
> >               dev_err(&chip->spi_dev->dev,
> > -                     "Invalid channel id %lu for ad7816.\n", data);
> > +                     "Invalid channel id %lu for %s.\n", data, indio_dev-
> > >name);
> >               return -EINVAL;
> >       }
>
> Hmm, maybe I'm missing something but the code just looks the same as before
> (from a functionality point of view)? I'm really not seeing any fix...
I might have to change it for readability. From my understanding, if
channel 7 is selected (AD7816_CS_MASK), it never enters the error path
whereas in the old code, if the chip were either ad7816 or ad7818, it would
end up returning an error because it skips all channels above either 0
or 1.

>
> Having said the above, not sure if grouping helps with readability. But I do
> agree with moving from string comparison to use chip->id. And we also have
> redundants 'else'
>
> - Nuno Sá
>