Re: [PATCH 04/10] iio: adc: stm32-dfsdm: Avoid dereferencing ->currentmode

[Jonathan Cameron <jic23@kernel.org>]

On Thu, 16 Dec 2021 09:22:35 +0100
Miquel Raynal <miquel.raynal@bootlin.com> wrote:

> Hi Alexandru,
> 
> ardeleanalex@gmail.com wrote on Thu, 16 Dec 2021 08:47:02 +0200:
> 
> > On Wed, Dec 15, 2021 at 10:03 PM Miquel Raynal
> > <miquel.raynal@bootlin.com> wrote:  
> > >
> > > This is an internal variable of the core, let's use the
> > > iio_buffer_enabled() helper which is exported for the following purpose:
> > > telling if the current mode is a buffered mode, which is precisely what
> > > this driver looks for.
> > >
> > > Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
> > > ---
> > >  drivers/iio/adc/stm32-dfsdm-adc.c | 5 ++---
> > >  1 file changed, 2 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/iio/adc/stm32-dfsdm-adc.c b/drivers/iio/adc/stm32-dfsdm-adc.c
> > > index 1cfefb3b5e56..a3b8827d3bbf 100644
> > > --- a/drivers/iio/adc/stm32-dfsdm-adc.c
> > > +++ b/drivers/iio/adc/stm32-dfsdm-adc.c
> > > @@ -466,8 +466,7 @@ static int stm32_dfsdm_channels_configure(struct iio_dev *indio_dev,
> > >          * In continuous mode, use fast mode configuration,
> > >          * if it provides a better resolution.
> > >          */
> > > -       if (adc->nconv == 1 && !trig &&
> > > -           (indio_dev->currentmode & INDIO_BUFFER_SOFTWARE)) {
> > > +       if (adc->nconv == 1 && !trig && iio_buffer_enabled(indio_dev)) {    
> > 
> > This may become tricky if other modes get added later.
> > STM does a relatively good job in updating and re-using their drivers
> > (even if some of them do look quirky sometimes).

Their hardware is crazy/complicated so tends to push the limits!

> > 
> > So, the question here would be: is "iio_buffer_enabled(indio_dev)"
> > going to be valid [in this place] once INDIO_BUFFER_TRIGGERED or
> > INDIO_BUFFER_HARDWARE get added?  
> 
> I would argue, is this a real problem? Today iio_buffer_enabled() seem
> to handle well what this driver is expecting. If tomorrow someone adds
> another mode, that is his/her responsibility to state "okay, this
> section is not common to all buffer styles *anymore*, so we need to do
> a more fine grained check against ->currentmodes than
> iio_buffer_enabled() does". In that case using the ->currentmodes
> getter would be the right way to go, but only at that particular
> moment, not today.

It should be isolated to this driver, so I think it is fine to use
the broader check today, but I'll leave this to the st folks as
it's their driver and I don't feel that strongly about it.

> 
> > 
> > I'd also ping some STM people for some feedback, acks or testing.

Definitely on this - they are an active bunch who do a great job of looking
after these drivers.  I've cc'd Fabrice. Make sure he (and possibly some
others are on v2 cc list).


> >   
> > >                 if (fl->flo[1].res >= fl->flo[0].res) {
> > >                         fl->fast = 1;
> > >                         flo = &fl->flo[1];
> > > @@ -562,7 +561,7 @@ static int stm32_dfsdm_filter_configure(struct iio_dev *indio_dev,
> > >                 cr1 = DFSDM_CR1_RCH(chan->channel);
> > >
> > >                 /* Continuous conversions triggered by SPI clk in buffer mode */
> > > -               if (indio_dev->currentmode & INDIO_BUFFER_SOFTWARE)
> > > +               if (iio_buffer_enabled(indio_dev))
> > >                         cr1 |= DFSDM_CR1_RCONT(1);
> > >
> > >                 cr1 |= DFSDM_CR1_RSYNC(fl->sync_mode);
> > > --
> > > 2.27.0
> > >    
> 
> 
> Thanks,
> Miquèl