linux-kernel - Re: [PATCH v2] meson saradc: add iio device attrib to switch channel 7 mux

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Message-ID: <ZHMxDHPBWQOJSuaZ@smile.fi.intel.com>
Date:   Sun, 28 May 2023 13:46:36 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     George Stark <gnstark@...rdevices.ru>
Cc:     jic23@...nel.org, lars@...afoo.de, neil.armstrong@...aro.org,
        khilman@...libre.com, jbrunet@...libre.com,
        martin.blumenstingl@...glemail.com, nuno.sa@...log.com,
        linux-iio@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-amlogic@...ts.infradead.org,
        kernel@...rdevices.ru
Subject: Re: [PATCH v2] meson saradc: add iio device attrib to switch channel
 7 mux

On Sun, May 28, 2023 at 12:48:54AM +0300, George Stark wrote:
> Patch adds two sysfs nodes: chan7_mux to set mux state
> and chan7_mux_available to show available mux states.
> Mux can be used to debug and calibrate adc by
> switching and measuring well-known inputs like GND, Vdd etc.

Thank you for an update, my comments below.

...

> ---

Missing changelog, what has been done in v2, how it's different to v1.

>  drivers/iio/adc/meson_saradc.c | 65 ++++++++++++++++++++++++++++++++++
>  1 file changed, 65 insertions(+)

...

> +static const char * const chan7_vol[] = {
> +	"gnd",
> +	"vdd/4",
> +	"vdd/2",
> +	"vdd*3/4",
> +	"vdd",
> +	"ch7_input",
> +};
> +
> +static ssize_t chan7_mux_show(struct device *dev, struct device_attribute *attr,
> +			      char *buf)
> +{
> +	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> +	struct meson_sar_adc_priv *priv = iio_priv(indio_dev);
> +	unsigned int index = priv->chan7_mux_sel;
> +
> +	if (index >= ARRAY_SIZE(chan7_vol))
> +		index = ARRAY_SIZE(chan7_vol) - 1;

I think this is incorrect and prone to error in the future in case this array
will be extended. What I would expect is to return something like "unknown".

> +	return sysfs_emit(buf, "%s\n", chan7_vol[index]);
> +}
> +
> +static ssize_t chan7_mux_store(struct device *dev,
> +			       struct device_attribute *attr,
> +			       const char *buf, size_t count)
> +{
> +	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> +	int i;
> +
> +	i = sysfs_match_string(chan7_vol, buf);
> +	if (i < 0)

> +		return -EINVAL;

Do not shadow the error code if it's not justified.

		return i;

> +	meson_sar_adc_set_chan7_mux(indio_dev, i);
> +	return count;
> +}

> +

Redundant blank line.

> +static IIO_DEVICE_ATTR_RW(chan7_mux, -1);
> +
> +static ssize_t chan7_mux_available_show(struct device *dev, struct device_attribute *attr,
> +			      char *buf)
> +{
> +	int i, len = 0;
> +
> +	for (i = 0; i < ARRAY_SIZE(chan7_vol); i++)
> +		len += sysfs_emit_at(buf, len, "%s ", chan7_vol[i]);
> +
> +	return len;
> +}

> +

Ditto.

> +static IIO_DEVICE_ATTR_RO(chan7_mux_available, -1);

-- 
With Best Regards,
Andy Shevchenko