linux-kernel - RE: [PATCH 10/16] iio: adc: max1027: Prevent single channel accesses during buffer reads

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Date:   Fri, 20 Aug 2021 07:30:07 +0000
From:   "Sa, Nuno" <Nuno.Sa@...log.com>
To:     "Sa, Nuno" <Nuno.Sa@...log.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>
CC:     Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 10/16] iio: adc: max1027: Prevent single channel accesses
 during buffer reads



> -----Original Message-----
> From: Sa, Nuno <Nuno.Sa@...log.com>
> Sent: Friday, August 20, 2021 9:21 AM
> To: Miquel Raynal <miquel.raynal@...tlin.com>; Jonathan Cameron
> <jic23@...nel.org>; Lars-Peter Clausen <lars@...afoo.de>
> Cc: Thomas Petazzoni <thomas.petazzoni@...tlin.com>; linux-
> iio@...r.kernel.org; linux-kernel@...r.kernel.org
> Subject: RE: [PATCH 10/16] iio: adc: max1027: Prevent single channel
> accesses during buffer reads
> 
> [External]
> 
> 
> 
> > -----Original Message-----
> > From: Miquel Raynal <miquel.raynal@...tlin.com>
> > Sent: Wednesday, August 18, 2021 1:12 PM
> > To: Jonathan Cameron <jic23@...nel.org>; Lars-Peter Clausen
> > <lars@...afoo.de>
> > Cc: Thomas Petazzoni <thomas.petazzoni@...tlin.com>; linux-
> > iio@...r.kernel.org; linux-kernel@...r.kernel.org; Miquel Raynal
> > <miquel.raynal@...tlin.com>
> > Subject: [PATCH 10/16] iio: adc: max1027: Prevent single channel
> > accesses during buffer reads
> >
> > [External]
> >
> > When hardware buffers are enabled (the cnvst pin being the
> trigger),
> > one
> > should not mess with the device state by requesting a single channel
> > read. Prevent it with a iio_buffer_enabled() check.
> >
> > Signed-off-by: Miquel Raynal <miquel.raynal@...tlin.com>
> > ---
> >  drivers/iio/adc/max1027.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/iio/adc/max1027.c b/drivers/iio/adc/max1027.c
> > index 223c9e4abd86..83526f3d7d3a 100644
> > --- a/drivers/iio/adc/max1027.c
> > +++ b/drivers/iio/adc/max1027.c
> > @@ -335,6 +335,8 @@ static int max1027_read_raw(struct iio_dev
> > *indio_dev,
> >
> >  	switch (mask) {
> >  	case IIO_CHAN_INFO_RAW:
> > +		if (iio_buffer_enabled(indio_dev))
> > +			return -EBUSY;
> 
> I guess 'iio_device_claim_direct_mode()' would be a better option
> here? There's nothing preventing this check to pass and then,
> concurrently
> someone enables the buffer...
> 

Taking a second look, it seems that this check is already done [1]? Am I missing
I missing something?

Also, I think we are returning with the 'st->lock' held...

[1]: https://elixir.bootlin.com/linux/latest/source/drivers/iio/adc/max1027.c#L247