Re: [PATCH V2] iio: ad_sigma_delta: Properly handle SPI bus locking vs CS assertion

[Jonathan Cameron <jic23@jic23.retrosnub.co.uk>]

On Tue, 26 Mar 2019 12:43:32 +0000
"Ardelean, Alexandru" <alexandru.Ardelean@analog.com> wrote:

> On Sun, 2019-03-24 at 17:47 +0000, Jonathan Cameron wrote:
> > [External]
> > 
> > 
> > On Tue, 19 Mar 2019 13:37:55 +0200
> > Alexandru Ardelean <alexandru.ardelean@analog.com> wrote:
> >   
> > > From: Lars-Peter Clausen <lars@metafoo.de>
> > > 
> > > For devices from the SigmaDelta family we need to keep CS low when
> > > doing a
> > > conversion, since the device will use the MISO line as a interrupt to
> > > indicate that the conversion is complete.
> > > 
> > > This is why the driver locks the SPI bus and when the SPI bus is locked
> > > keeps as long as a conversion is going on. The current implementation
> > > gets
> > > one small detail wrong though. CS is only de-asserted after the SPI bus
> > > is
> > > unlocked. This means it is possible for a different SPI device on the
> > > same
> > > bus to send a message which would be wrongfully be addressed to the
> > > SigmaDelta device as well. Make sure that the last SPI transfer that is
> > > done while holding the SPI bus lock de-asserts the CS signal.
> > > 
> > > Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
> > > Signed-off-by: Alexandru Ardelean <Alexandru.Ardelean@analog.com>  
> > 
> > Hi Alex,
> > 
> > So, it's a fix for a long existing problem.  Do we have anyone who
> > has experienced it?  I'm trying to judge whether this is stable material
> > or not.  If it is stable material, do you want to have a go at
> > identifying
> > a patch for the Fixes tag?  
> 
> So I actually forgot to do the preparation before cherry-picking this one
> [i.e. whether it should have a Fixes tag or not].
> Sorry abou that.
> 
> This change is more in the context of some non-upstream functionality for
> the SigmaDelta. i.e. it's a fix, but it's more important for a
> functionality that will be added later.
> 
> There aren't any people that have experienced issues with the mainline
> version of the ad_sigma_delta drivers that I know of.
> 
> Bottom line is, we can skip adding this one to stable.
> 
Applied to the togreg branch of iio.git and pushed out as testing for
the autobuilders to play with it.

Thanks,

Jonathan

> Thanks
> Alex
> 
> 
> > Patch looks good.
> > 
> > Jonathan
> >   
> > > ---
> > > 
> > > Changelog v1 -> v2:
> > > * added my S-o-B line
> > > 
> > >  drivers/iio/adc/ad_sigma_delta.c       | 16 +++++++++++-----
> > >  include/linux/iio/adc/ad_sigma_delta.h |  1 +
> > >  2 files changed, 12 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/drivers/iio/adc/ad_sigma_delta.c
> > > b/drivers/iio/adc/ad_sigma_delta.c
> > > index ff5f2da2e1b1..af6cbc683214 100644
> > > --- a/drivers/iio/adc/ad_sigma_delta.c
> > > +++ b/drivers/iio/adc/ad_sigma_delta.c
> > > @@ -62,7 +62,7 @@ int ad_sd_write_reg(struct ad_sigma_delta
> > > *sigma_delta, unsigned int reg,
> > >       struct spi_transfer t = {
> > >               .tx_buf         = data,
> > >               .len            = size + 1,
> > > -             .cs_change      = sigma_delta->bus_locked,
> > > +             .cs_change      = sigma_delta->keep_cs_asserted,
> > >       };
> > >       struct spi_message m;
> > >       int ret;
> > > @@ -217,6 +217,7 @@ static int ad_sd_calibrate(struct ad_sigma_delta
> > > *sigma_delta,
> > > 
> > >       spi_bus_lock(sigma_delta->spi->master);
> > >       sigma_delta->bus_locked = true;
> > > +     sigma_delta->keep_cs_asserted = true;
> > >       reinit_completion(&sigma_delta->completion);
> > > 
> > >       ret = ad_sigma_delta_set_mode(sigma_delta, mode);
> > > @@ -234,9 +235,10 @@ static int ad_sd_calibrate(struct ad_sigma_delta
> > > *sigma_delta,
> > >               ret = 0;
> > >       }
> > >  out:
> > > +     sigma_delta->keep_cs_asserted = false;
> > > +     ad_sigma_delta_set_mode(sigma_delta, AD_SD_MODE_IDLE);
> > >       sigma_delta->bus_locked = false;
> > >       spi_bus_unlock(sigma_delta->spi->master);
> > > -     ad_sigma_delta_set_mode(sigma_delta, AD_SD_MODE_IDLE);
> > > 
> > >       return ret;
> > >  }
> > > @@ -289,6 +291,7 @@ int ad_sigma_delta_single_conversion(struct iio_dev
> > > *indio_dev,
> > > 
> > >       spi_bus_lock(sigma_delta->spi->master);
> > >       sigma_delta->bus_locked = true;
> > > +     sigma_delta->keep_cs_asserted = true;
> > >       reinit_completion(&sigma_delta->completion);
> > > 
> > >       ad_sigma_delta_set_mode(sigma_delta, AD_SD_MODE_SINGLE);
> > > @@ -298,9 +301,6 @@ int ad_sigma_delta_single_conversion(struct iio_dev
> > > *indio_dev,
> > >       ret = wait_for_completion_interruptible_timeout(
> > >                       &sigma_delta->completion, HZ);
> > > 
> > > -     sigma_delta->bus_locked = false;
> > > -     spi_bus_unlock(sigma_delta->spi->master);
> > > -
> > >       if (ret == 0)
> > >               ret = -EIO;
> > >       if (ret < 0)
> > > @@ -321,7 +321,10 @@ int ad_sigma_delta_single_conversion(struct
> > > iio_dev *indio_dev,
> > >               sigma_delta->irq_dis = true;
> > >       }
> > > 
> > > +     sigma_delta->keep_cs_asserted = false;
> > >       ad_sigma_delta_set_mode(sigma_delta, AD_SD_MODE_IDLE);
> > > +     sigma_delta->bus_locked = false;
> > > +     spi_bus_unlock(sigma_delta->spi->master);
> > >       mutex_unlock(&indio_dev->mlock);
> > > 
> > >       if (ret)
> > > @@ -358,6 +361,8 @@ static int ad_sd_buffer_postenable(struct iio_dev
> > > *indio_dev)
> > > 
> > >       spi_bus_lock(sigma_delta->spi->master);
> > >       sigma_delta->bus_locked = true;
> > > +     sigma_delta->keep_cs_asserted = true;
> > > +
> > >       ret = ad_sigma_delta_set_mode(sigma_delta,
> > > AD_SD_MODE_CONTINUOUS);
> > >       if (ret)
> > >               goto err_unlock;
> > > @@ -386,6 +391,7 @@ static int ad_sd_buffer_postdisable(struct iio_dev
> > > *indio_dev)
> > >               sigma_delta->irq_dis = true;
> > >       }
> > > 
> > > +     sigma_delta->keep_cs_asserted = false;
> > >       ad_sigma_delta_set_mode(sigma_delta, AD_SD_MODE_IDLE);
> > > 
> > >       sigma_delta->bus_locked = false;
> > > diff --git a/include/linux/iio/adc/ad_sigma_delta.h
> > > b/include/linux/iio/adc/ad_sigma_delta.h
> > > index 7e84351fa2c0..6e9fb1932dde 100644
> > > --- a/include/linux/iio/adc/ad_sigma_delta.h
> > > +++ b/include/linux/iio/adc/ad_sigma_delta.h
> > > @@ -69,6 +69,7 @@ struct ad_sigma_delta {
> > >       bool                    irq_dis;
> > > 
> > >       bool                    bus_locked;
> > > +     bool                    keep_cs_asserted;
> > > 
> > >       uint8_t                 comm;
> > >   
> > 
> >