Re: [PATCH] staging: iio: ade7753: replace mlock with driver private lock

[Jonathan Cameron <jic23@kernel.org>]

On Wed, 27 Sep 2017 20:27:09 +0530
Himanshi Jain <himshijain.hj@gmail.com> wrote:

> On Sun, Sep 24, 2017 at 7:47 PM, Jonathan Cameron <jic23@kernel.org> wrote:
> > On Mon, 18 Sep 2017 12:29:52 +0530
> > Himanshi Jain <himshijain.hj@gmail.com> wrote:
> >  
> >> Replace driver usage of mlock with driver private lock to meet the new
> >> model where usage of iio_dev->mlock is being redefined as protecting
> >> operating mode changes(changes between BUFFER* and DIRECT modes).
> >>
> >> Signed-off-by: Himanshi Jain <himshijain.hj@gmail.com>  
> >
> > A well presented patch making a sensible change.  My only thought here
> > is that ultimately we could cover bother the buffer protection and
> > the state protection with a single lock.
> >
> > Hmm. The new lock (as was the old mlock code) is providing protection
> > to ensure we end up with consistent state when changing the
> > sampling frequency between the sampling frequency and the
> > bus clock speed (which has different maximum values depending
> > on the current sampling frequency). In similar cases we have
> > expanded the meaning on the buffer lock to fulfil both roles
> > - that could be done here as well, although you have to be careful
> > about deadlocks.
> >  
> 
> I have understood how to use a single lock for both the purposes as you have
> quoted in Katie's patch too i.e. by making an unlocked version of the function
> ade7753_spi_write_reg_16(). And since the function is not publicly available
> to be used, an unlocked version will not create any issue(which is why I am
> assuming, we are not using nested locks - Please correct me if I am wrong.)
> 
> I will submit a new patch with a single lock.

That's great, but please do it on top of your previous patch as that is now
in a non rebasing tree.

Jonathan

> 
> > On reflection I think this patch is worthwhile applying even
> > if this new lock gets dropped again in some later rework of this
> > driver.
> >
> > Applied to the togreg branch of iio.git and pushed out as testing for
> > the autobuilders to play with it.
> >  
> 
> Thank you for reviewing and applying the patch and guiding for a better logical
> solution.
> 
> > Thanks,
> >
> > Jonathan  
> >> ---
> >>  drivers/staging/iio/meter/ade7753.c | 7 +++++--
> >>  1 file changed, 5 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/staging/iio/meter/ade7753.c b/drivers/staging/iio/meter/ade7753.c
> >> index ce26abdea..745c5a6 100644
> >> --- a/drivers/staging/iio/meter/ade7753.c
> >> +++ b/drivers/staging/iio/meter/ade7753.c
> >> @@ -81,10 +81,12 @@
> >>   * @tx:         transmit buffer
> >>   * @rx:         receive buffer
> >>   * @buf_lock:       mutex to protect tx and rx
> >> + * @lock:    protect sensor data
> >>   **/
> >>  struct ade7753_state {
> >>       struct spi_device   *us;
> >>       struct mutex        buf_lock;
> >> +     struct mutex        lock; /* protect sensor data */
> >>       u8          tx[ADE7753_MAX_TX] ____cacheline_aligned;
> >>       u8          rx[ADE7753_MAX_RX];
> >>  };
> >> @@ -483,7 +485,7 @@ static ssize_t ade7753_write_frequency(struct device *dev,
> >>       if (!val)
> >>               return -EINVAL;
> >>
> >> -     mutex_lock(&indio_dev->mlock);
> >> +     mutex_lock(&st->lock);
> >>
> >>       t = 27900 / val;
> >>       if (t > 0)
> >> @@ -504,7 +506,7 @@ static ssize_t ade7753_write_frequency(struct device *dev,
> >>       ret = ade7753_spi_write_reg_16(dev, ADE7753_MODE, reg);
> >>
> >>  out:
> >> -     mutex_unlock(&indio_dev->mlock);
> >> +     mutex_unlock(&st->lock);
> >>
> >>       return ret ? ret : len;
> >>  }
> >> @@ -580,6 +582,7 @@ static int ade7753_probe(struct spi_device *spi)
> >>       st = iio_priv(indio_dev);
> >>       st->us = spi;
> >>       mutex_init(&st->buf_lock);
> >> +     mutex_init(&st->lock);
> >>
> >>       indio_dev->name = spi->dev.driver->name;
> >>       indio_dev->dev.parent = &spi->dev;  
> >  
> --
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