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

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Date:   Thu, 30 Nov 2023 15:50:46 -0600
From:   David Lechner <dlechner@...libre.com>
To:     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 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. :-)

>  #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.