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

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Message-ID: <6ce5ba44403d2fddbcd35384ce6444f9719c788e.camel@baylibre.com>
Date: Thu, 30 Oct 2025 12:03:58 +0100
From: Francesco Lavra <flavra@...libre.com>
To: Andy Shevchenko <andriy.shevchenko@...el.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, 2025-10-30 at 09:57 +0200, Andy Shevchenko wrote:
> 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?

Will add

> 
> > +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.

Will 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...

This function returns a pointer to the struct iio_dev it allocates and
initializes; if there are any errors, it returns NULL. What kind of comment
do you expect here? It seems obvious that it's returning NULL because of an
allocation error.

> 
> > +       for (i = 0; i < 3; i++) {
> 
> 3 might need to be defined.

Will make an enum to replace the ST_LSM6DSX_CHAN_COUNT #define, and use an
enum value instead of 3.

> 
> > +               if (st_lsm6dsx_chan_init(channels, hw, id, i) < 0)
> > +                       return NULL;
> > +       }
> 
> + blank line
> 
> ...and perhaps here to explain what's going on here.

Same here, what comment do you expect?

> > +       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;
>