linux-kernel - Re: [PATCH 1/9] iio: imu: st_lsm6dsx: dynamically initialize iio_chan

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Message-ID: <aQMaaHWjgC2GMGmj@smile.fi.intel.com>
Date: Thu, 30 Oct 2025 09:57:28 +0200
From: Andy Shevchenko <andriy.shevchenko@...el.com>
To: Francesco Lavra <flavra@...libre.com>
Cc: Lorenzo Bianconi <lorenzo@...nel.org>,
	Jonathan Cameron <jic23@...nel.org>,
	David Lechner <dlechner@...libre.com>,
	Nuno Sá <nuno.sa@...log.com>,
	Andy Shevchenko <andy@...nel.org>, linux-iio@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/9] iio: imu: st_lsm6dsx: dynamically initialize
 iio_chan_spec data

On Thu, Oct 30, 2025 at 08:27:44AM +0100, Francesco Lavra wrote:
> Using the ST_LSM6DSX_CHANNEL_ACC() macro as a static initializer
> for the iio_chan_spec struct arrays makes all sensors advertise
> channel event capabilities regardless of whether they actually
> support event generation. And if userspace tries to configure
> accelerometer wakeup events on a sensor device that does not
> support them (e.g. LSM6DS0), st_lsm6dsx_write_event() dereferences
> a NULL pointer when trying to write to the wakeup register.
> Replace usage of the ST_LSM6DSX_CHANNEL_ACC() and
> ST_LSM6DSX_CHANNEL() macros with dynamic allocation and
> initialization of struct iio_chan_spec arrays, where the
> st_lsm6dsx_event structure is only used for sensors that support
> wakeup events; besides fixing the above bug, this serves as a
> preliminary step for adding support for more event types.


Sounds like a bug fix. Fixes tag?

...

> +static int st_lsm6dsx_chan_init(struct iio_chan_spec *channels, struct st_lsm6dsx_hw *hw,
> +				enum st_lsm6dsx_sensor_id id, int index)
> +{
> +	struct iio_chan_spec *chan = &channels[index];
> +
> +	chan->type = (id == ST_LSM6DSX_ID_ACC) ? IIO_ACCEL : IIO_ANGL_VEL;
> +	chan->address = hw->settings->chan_addr_base[id] + index * ST_LSM6DSX_CHAN_SIZE;
> +	chan->modified = 1;
> +	chan->channel2 = IIO_MOD_X + index;
> +	chan->info_mask_separate = BIT(IIO_CHAN_INFO_RAW);
> +	chan->info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE);
> +	chan->info_mask_shared_by_all = BIT(IIO_CHAN_INFO_SAMP_FREQ);
> +	chan->scan_index = index;
> +	chan->scan_type.sign = 's';
> +	chan->scan_type.realbits = 16;
> +	chan->scan_type.storagebits = 16;
> +	chan->scan_type.endianness = IIO_LE;
> +	chan->ext_info = st_lsm6dsx_ext_info;

+ blank line

> +	if (id == ST_LSM6DSX_ID_ACC) {
> +		if (hw->settings->event_settings.wakeup_reg.addr) {
> +			chan->event_spec = &st_lsm6dsx_event;
> +			chan->num_event_specs = 1;
> +		}
> +	}

if (foo) { if (bar) {}  } == if (foo && bar).

Based on this I'm in doubt what to suggest here as to me sounds like those
couple of lines might deserve for a helper.

Hence two options:
1) do an equivalent conditional and reduce indentation level;
2) do a helper with the inner conditional.

+ blank line

> +	return 0;
> +}

...

> +	channels = devm_kzalloc(hw->dev, sizeof(*channels) * ST_LSM6DSX_CHAN_COUNT, GFP_KERNEL);

devm_kcalloc()

> +	if (!channels)
> +		return NULL;

I would expect comment here...

> +	for (i = 0; i < 3; i++) {

3 might need to be defined.

> +		if (st_lsm6dsx_chan_init(channels, hw, id, i) < 0)
> +			return NULL;
> +	}

+ blank line

...and perhaps here to explain what's going on here.

> +	channels[3].type = IIO_TIMESTAMP;
> +	channels[3].channel = -1;
> +	channels[3].scan_index = 3;
> +	channels[3].scan_type.sign = 's';
> +	channels[3].scan_type.realbits = 64;
> +	channels[3].scan_type.storagebits = 64;

+ blank line.

>  	iio_dev->modes = INDIO_DIRECT_MODE;
>  	iio_dev->available_scan_masks = st_lsm6dsx_available_scan_masks;
> -	iio_dev->channels = hw->settings->channels[id].chan;
> -	iio_dev->num_channels = hw->settings->channels[id].len;
> +	iio_dev->channels = channels;
> +	iio_dev->num_channels = ST_LSM6DSX_CHAN_COUNT;

-- 
With Best Regards,
Andy Shevchenko