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From:   Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Date:   Mon, 29 May 2023 22:04:18 +0200
Message-ID: <CAFBinCA=earf119bN7ohmTQGDzSMeV9qcL8RU9DUYe0195H5=Q@mail.gmail.com>
Subject: Re: [PATCH v2] meson saradc: add iio device attrib to switch channel
 7 mux
To:     George Stark <GNStark@sberdevices.ru>
Cc:     Jonathan Cameron <jic23@kernel.org>,
        "lars@metafoo.de" <lars@metafoo.de>,
        "neil.armstrong@linaro.org" <neil.armstrong@linaro.org>,
        "khilman@baylibre.com" <khilman@baylibre.com>,
        "jbrunet@baylibre.com" <jbrunet@baylibre.com>,
        "andriy.shevchenko@linux.intel.com" 
        <andriy.shevchenko@linux.intel.com>,
        "nuno.sa@analog.com" <nuno.sa@analog.com>,
        "linux-iio@vger.kernel.org" <linux-iio@vger.kernel.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-amlogic@lists.infradead.org" 
        <linux-amlogic@lists.infradead.org>, kernel <kernel@sberdevices.ru>
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Hi George,

On Sun, May 28, 2023 at 11:52=E2=80=AFPM George Stark <GNStark@sberdevices.=
ru> wrote:
[...]
> > Based on the limited description we have here, I'm not understanding wh=
y
> > you don't just express this as a set of channels. One channel per mux
> > setting, with the in_voltageX_label providing the information on what t=
he
> > channel is connected to.
> >
> > This is an interesting facility, so good to enable for high precision c=
alibration
> > but we still want to map it to standards signals.  Userspace doesn't
> > care that these are all being measured via the same input 7 - which
> > is itself probably an input to a MUX.
> >
> > Jonathan
>
> Hello Jonathan
>
> Thanks for the review.
>
> Your idea of exposing the mux setting as iio channels is very
> interesting and at least worth trying.
> The sysfs approach was chosen because of the code changes are simple and
> neat (compare to channels approach).
> Also calibration by using those mux inputs are already supported in the
> driver (performed at probe stage) so I expect very special usecases for
> those mux settings like debug or device production stage tests. In those
> usescases hardware specific knowledge is required anyway.
Another downside to the debugfs approach is user support:
If someone reports odd values on ADC channel 7 then we need to make
sure to double check if the mux has been altered from userspace (the
calibration during initialization ensures to leave channel 7 in a
consistent state, while a user may change the mux, forget about it and
then complain that values are wrong).


Best regards,
Martin