Re: [PATCH 2/2] iio: imu: st_lsm6dsx: add iio trigger and buffer support

[Lorenzo Bianconi <lorenzo@kernel.org>]

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> On Tue,  7 May 2019 10:02:25 +0200
> Sean Nyekjaer <sean@geanix.com> wrote:
> 
> > This adds support for using iio triggers, this is needed because
> > our hardware guys forgot to connect the irq pins from imu device
> > to the SoC.
> > 
> > Signed-off-by: Sean Nyekjaer <sean@geanix.com>
> Hi Sean
> 
> A small question on the size of the buffer needed inline.  Otherwise looks
> good to me.

Hi Sean,

this patch does not make sense to me since running st_lsm6dsx_read_oneshot
you need to wait to power up the device (and you will power it down at the
end). I guess you will not be able to read at a given ODR (e.g. 416Hz).
Moreover you can't read from the hw fifo without the irq line since
you need to read a full pattern from it in order to maintain the alignment.
From my point of view you have 2 possibility:
- poll the output registers from userspace (this is what you are actually
  doing from inside the kernel, what is the advantage of doing so?)
- fix the hw bug

Moreover if I read the patch correctly it has a NULL pointer dereference bug
since hw->iio_devs[i] can be NULL (e.g. if sensor hub is disabled)

Regards,
Lorenzo

> > ---
> >  drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c | 37 ++++++++++++++++++++
> >  1 file changed, 37 insertions(+)
> > 
> > diff --git a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
> > index 1ca69598678f..65ab853202de 100644
> > --- a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
> > +++ b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
> > @@ -40,8 +40,11 @@
> >  #include <linux/kernel.h>
> >  #include <linux/module.h>
> >  #include <linux/delay.h>
> > +#include <linux/iio/buffer.h>
> >  #include <linux/iio/iio.h>
> >  #include <linux/iio/sysfs.h>
> > +#include <linux/iio/trigger_consumer.h>
> > +#include <linux/iio/triggered_buffer.h>
> >  #include <linux/pm.h>
> >  #include <linux/regmap.h>
> >  #include <linux/bitfield.h>
> > @@ -945,6 +948,30 @@ static int st_lsm6dsx_init_hw_timer(struct st_lsm6dsx_hw *hw)
> >  	return 0;
> >  }
> >  
> > +static irqreturn_t st_lsm6dsx_trigger_handler(int irq, void *p)
> > +{
> > +	struct iio_poll_func *pf = p;
> > +	struct iio_dev *indio_dev = pf->indio_dev;
> > +	struct st_lsm6dsx_sensor *sensor = iio_priv(indio_dev);
> > +	u16 buffer[4 * sizeof(s64)/sizeof(u16)];
> The size may well be correct, but that particular way of expressing it doesn't make
> it terribly clear.
> 
> It seems a bit large... You need the space for the timestamp, so it needs to be
> padded to a u64, but that would still require your other channels to need
> more than 2*sizeof(s64)/sizeof(u16) u16s which is 9 or more of them.
> 
> > +	int tmp, bit;
> > +
> > +	memset(buffer, 0, sizeof(buffer));
> > +
> > +	for_each_set_bit(bit, indio_dev->active_scan_mask, indio_dev->masklength) {
> > +		st_lsm6dsx_read_oneshot(sensor,
> > +					indio_dev->channels[bit].address, &tmp);
> > +		buffer[bit] = tmp;
> > +	}
> > +
> > +	iio_push_to_buffers_with_timestamp(indio_dev, buffer,
> > +					   iio_get_time_ns(indio_dev));
> > +
> > +	iio_trigger_notify_done(indio_dev->trig);
> > +
> > +	return IRQ_HANDLED;
> > +}
> > +
> >  static int st_lsm6dsx_init_device(struct st_lsm6dsx_hw *hw)
> >  {
> >  	u8 drdy_int_reg;
> > @@ -1093,6 +1120,16 @@ int st_lsm6dsx_probe(struct device *dev, int irq, int hw_id, const char *name,
> >  		err = st_lsm6dsx_fifo_setup(hw);
> >  		if (err < 0)
> >  			return err;
> > +	} else {
> > +		for (i = 0; i < ST_LSM6DSX_ID_MAX; i++) {
> > +			err = devm_iio_triggered_buffer_setup(hw->dev,
> > +					hw->iio_devs[i], NULL,
> > +					st_lsm6dsx_trigger_handler, NULL);

I guess hw->iio_devs[i] can be NULL here

> > +			if (err < 0) {
> > +				dev_err(hw->dev, "iio triggered buffer setup failed\n");
> > +				return err;
> > +			}
> > +		}
> >  	}
> >  
> >  	for (i = 0; i < ST_LSM6DSX_ID_MAX; i++) {
> 


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