linux-kernel - Re: [PATCH v7 05/10] iio: adc: sun20i-gpadc: Use adc-helpers

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Message-ID: <Z9LQ0O34EUM8WZku@smile.fi.intel.com>
Date: Thu, 13 Mar 2025 14:34:24 +0200
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Matti Vaittinen <mazziesaccount@...il.com>
Cc: Matti Vaittinen <matti.vaittinen@...rohmeurope.com>,
	Jonathan Cameron <jic23@...nel.org>,
	Lars-Peter Clausen <lars@...afoo.de>, Chen-Yu Tsai <wens@...e.org>,
	Jernej Skrabec <jernej.skrabec@...il.com>,
	Samuel Holland <samuel@...lland.org>, Nuno Sa <nuno.sa@...log.com>,
	David Lechner <dlechner@...libre.com>,
	Javier Carrasco <javier.carrasco.cruz@...il.com>,
	Olivier Moysan <olivier.moysan@...s.st.com>,
	Guillaume Stols <gstols@...libre.com>,
	Dumitru Ceclan <mitrutzceclan@...il.com>,
	Trevor Gamblin <tgamblin@...libre.com>,
	Matteo Martelli <matteomartelli3@...il.com>,
	Alisa-Dariana Roman <alisadariana@...il.com>,
	linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-sunxi@...ts.linux.dev
Subject: Re: [PATCH v7 05/10] iio: adc: sun20i-gpadc: Use adc-helpers

On Thu, Mar 13, 2025 at 09:18:49AM +0200, Matti Vaittinen wrote:
> The new devm_iio_adc_device_alloc_chaninfo_se() -helper is intended to
> help drivers avoid open-coding the for_each_node -loop for getting the
> channel IDs. The helper provides standard way to detect the ADC channel
> nodes (by the node name), and a standard way to convert the "reg"
> -properties to channel identification numbers, used in the struct
> iio_chan_spec. Furthermore, the helper can optionally check the found
> channel IDs are smaller than given maximum. This is useful for callers
> which later use the IDs for example for indexing a channel data array.
> 
> The original driver treated all found child nodes as channel nodes. The
> new helper requires channel nodes to be named channel[@N]. This should
> help avoid problems with devices which may contain also other but ADC
> child nodes. Quick grep from arch/* with the sun20i-gpadc's compatible
> string didn't reveal any in-tree .dts with channel nodes named
> otherwise. Also, same grep shows all the in-tree .dts seem to have
> channel IDs between 0..num of channels.
> 
> Use the new helper.

...

> +	num_channels = devm_iio_adc_device_alloc_chaninfo_se(dev,
> +				&sun20i_gpadc_chan_template, -1, &channels);
> +	if (num_channels < 0)
> +		return num_channels;
> +
>  	if (num_channels == 0)
>  		return dev_err_probe(dev, -ENODEV, "no channel children\n");

Note, this what I would expected in your helper to see, i.e. separated cases
for < 0 (error code) and == 0, no channels.

Also, are all users going to have this check? Usually in other similar APIs
we return -ENOENT. And user won't need to have an additional check in case of
0 being considered as an error case too.




-- 
With Best Regards,
Andy Shevchenko