Re: [PATCH 3/8] iio: adc: ad9467: add mutex to struct ad9467_state

["Nuno Sá" <noname.nuno@gmail.com>]

On Wed, 2023-12-06 at 16:27 -0600, David Lechner wrote:
> On Tue, Dec 5, 2023 at 11:06 AM Nuno Sa via B4 Relay
> <devnull+nuno.sa.analog.com@kernel.org> wrote:
> > 
> > From: Nuno Sa <nuno.sa@analog.com>
> > 
> > When calling ad9467_set_scale(), multiple calls to ad9467_spi_write()
> > are done which means we need to properly protect the whole operation so
> > we are sure we will be in a sane state if two concurrent calls occur.
> 
> 
> ad9467_outputmode_set() also has multiple calls to ad9467_spi_write().
> Does it need similar protection?
> 

Just called during probe (of the axi-adc driver) before registering the IIO device.
We should not need the lock in there (for now).

> > 
> > Fixes: ad6797120238 ("iio: adc: ad9467: add support AD9467 ADC")
> > Signed-off-by: Nuno Sa <nuno.sa@analog.com>
> > ---
> >  drivers/iio/adc/ad9467.c | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/iio/adc/ad9467.c b/drivers/iio/adc/ad9467.c
> > index 0f2dce730a0a..badbef2ce9f8 100644
> > --- a/drivers/iio/adc/ad9467.c
> > +++ b/drivers/iio/adc/ad9467.c
> > @@ -4,8 +4,9 @@
> >   *
> >   * Copyright 2012-2020 Analog Devices Inc.
> >   */
> > -
> > +#include <linux/cleanup.h>
> >  #include <linux/module.h>
> > +#include <linux/mutex.h>
> >  #include <linux/device.h>
> >  #include <linux/kernel.h>
> >  #include <linux/slab.h>
> > @@ -121,6 +122,8 @@ struct ad9467_state {
> >         unsigned int                    output_mode;
> > 
> >         struct gpio_desc                *pwrdown_gpio;
> > +       /* ensure consistent state obtained on multiple related accesses */
> > +       struct mutex                    lock;
> >  };
> > 
> >  static int ad9467_spi_read(struct spi_device *spi, unsigned int reg)
> > @@ -161,6 +164,7 @@ static int ad9467_reg_access(struct adi_axi_adc_conv *conv,
> > unsigned int reg,
> >         int ret;
> > 
> >         if (readval == NULL) {
> > +               guard(mutex)(&st->lock);
> >                 ret = ad9467_spi_write(spi, reg, writeval);
> >                 if (ret)
> >                         return ret;
> > @@ -310,6 +314,7 @@ static int ad9467_set_scale(struct adi_axi_adc_conv *conv,
> > int val, int val2)
> >                 if (scale_val[0] != val || scale_val[1] != val2)
> >                         continue;
> > 
> > +               guard(mutex)(&st->lock);
> 
> Why is the guard inside of the for loop instead of outside?
> 
> __ad9467_get_scale() called in this loop calls ad9467_spi_read() too,

Hmm, am I missing something? __ad9467_get_scale() is not doing any spi access, is it?
I think you made confusion with the version without underscore...

- Nuno Sá
>