Re: [PATCH] iio: magnetometer: ak8975: ensure device is awake for buffered capture

[Joshua Crofts]

On Wed, 13 May 2026 at 22:40, Andy Shevchenko
<andriy.shevchenko@xxxxxxxxx> wrote:
>
> On Wed, May 13, 2026 at 04:35:52PM +0200, Joshua Crofts via B4 Relay wrote:
> > Currently, the ak8975_start_read_axis() can be called while the device
> > is autosuspended, causing two issues:
> >
> > 1. I2C transfers in the aforementioned function will fail or timeout
> > because ak8975_runtime_suspend() disables the device regulators.
> > 2. Since ak8975_fill_buffer() does not hold runtime references,
> > ak8975_runtime_suspend() can run concurrently, and since PM callbacks
> > do not use a locking mechanism, it may cause a race accessing the
> > control register via the I2C bus.
> >
> > Fix this issue by adding struct iio_buffer_setup_ops that contains
> > preenable and postdisable functions to ensure correct that device is
> > powered on when running a buffered capture.
>
> I think Suggested-by: Jonathan is appropriate here.
>
> ...
>
> > +static int ak8975_buffer_preenable(struct iio_dev *indio_dev)
> > +{
> > +     struct ak8975_data *data = iio_priv(indio_dev);
> > +     struct device *dev = &data->client->dev;
>
> Not sure if actually may use indio_dev->dev.parent here instead of this, but at
> least this one is robust against changing parent-child relations).

It being robust was my intention, considering this will be backported at some
point.

-- 
Kind regards

CJD