Re: [PATCH v3 4/5] iio: pressure: bmp280: Add support for BMP380 sensor family

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

> > > +
> > > +static int bmp380_read_calib(struct bmp280_data *data, unsigned int chip)
> > > +{
> > > +       int ret;
> > > +       struct bmp380_calib *calib = &data->calib.bmp380;
> > > +       u8 buf[BMP380_CALIB_REG_COUNT];  
> > 
> > I'd missed this previously but for SPI drivers, we should be providing
> > regmap_bulk accesses with DMA safe buffers.  That means they can't be on the
> > stack and need to be appropriately aligned IIO_DMA_MINALIGN as part of
> > the *data structure.
> > 
> > Last time I checked the SPI regmap implementation doesn't currently use
> > the buffers directly but it has in the past and may do again in the future 
> > - hence we should be careful to allow for that.
> >   
> 
> As we only use this buffer once to store temporally the calibration data to
> parse, I would like to avoid adding extra overhead to the device data struct.
> I've been consulting on DMA rules and safety, and if I understood correctly
> (listed the sources below), it should be safe to use a buffer allocated at
> runtime with kmalloc, right?

Yes. That works too.

>  * https://elinux.org/images/0/03/20181023-Wolfram-Sang-ELCE18-
>    safe_dma_buffers.pdf
>  * https://linux-arm-kernel.infradead.narkive.com/vyJqy0RQ/question-devm-
>    kmalloc-for-dma
> 
> Thanks in advance,
> Angel