linux-kernel - Re: [PATCH 06/12] iio: adc: ad9467: add mutex to struct ad9467

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Date:   Fri, 01 Dec 2023 09:49:38 +0100
From:   Nuno Sá <noname.nuno@...il.com>
To:     David Lechner <dlechner@...libre.com>, nuno.sa@...log.com
Cc:     linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-iio@...r.kernel.org,
        Olivier MOYSAN <olivier.moysan@...s.st.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Michael Hennerich <Michael.Hennerich@...log.com>
Subject: Re: [PATCH 06/12] iio: adc: ad9467: add mutex to struct ad9467_state

On Thu, 2023-11-30 at 15:50 -0600, David Lechner wrote:
> On Tue, Nov 21, 2023 at 4:17 AM Nuno Sa via B4 Relay
> <devnull+nuno.sa.analog.com@...nel.org> wrote:
> > 
> > From: Nuno Sa <nuno.sa@...log.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.
> > 
> > Fixes: ad6797120238 ("iio: adc: ad9467: add support AD9467 ADC")
> > Signed-off-by: Nuno Sa <nuno.sa@...log.com>
> > ---
> >  drivers/iio/adc/ad9467.c | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/iio/adc/ad9467.c b/drivers/iio/adc/ad9467.c
> > index 04474dbfa631..91821dee03b7 100644
> > --- a/drivers/iio/adc/ad9467.c
> > +++ b/drivers/iio/adc/ad9467.c
> > @@ -4,7 +4,7 @@
> >   *
> >   * Copyright 2012-2020 Analog Devices Inc.
> >   */
> > -
> > +#include <linux/cleanup.h>
> >  #include <linux/module.h>
> >  #include <linux/mutex.h>
> 
> Ah, the case of the misplaced header from the previous patch is solved. :-)
> 

Yeps, it needs to be in this patch :)

> >  #include <linux/device.h>
> > @@ -122,6 +122,8 @@ struct ad9467_state {
> >         unsigned int                    output_mode;
> > 
> >         struct gpio_desc                *pwrdown_gpio;
> > +       /* protect against concurrent accesses to the device */
> > +       struct mutex                    lock;
> >  };
> > 
> >  static int ad9467_spi_read(struct spi_device *spi, unsigned int reg)
> > @@ -162,6 +164,7 @@ static int ad9467_reg_access(struct adi_axi_adc_conv *conv,
> > unsigned int reg,
> >         int ret;
> > 
> >         if (!readval) {
> > +               guard(mutex)(&st->lock);
> >                 ret = ad9467_spi_write(spi, reg, writeval);
> >                 if (ret)
> >                         return ret;
> > @@ -310,6 +313,7 @@ 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);
> >                 ret = ad9467_spi_write(st->spi, AN877_ADC_REG_VREF,
> >                                        info->scale_table[i][1]);
> >                 if (ret < 0)
> > 
> > --
> > 2.42.1
> > 
> > 
> 
> Alternately, this could probably be solved with spi_bus_lock/unlock
> and spi_sync_locked rather than introducing a new mutex.

Hmm, typically you just have your own lock. No reason to lock the spi bus. And I also
have some plans to eventually change this to regmap :)

- Nuno Sá