Re: [PATCH 06/12] iio: adc: ad9467: add mutex to struct ad9467_state

[Jonathan Cameron <jic23@kernel.org>]

On Tue, 21 Nov 2023 11:20:19 +0100
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.
> 
> Fixes: ad6797120238 ("iio: adc: ad9467: add support AD9467 ADC")
> Signed-off-by: Nuno Sa <nuno.sa@analog.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>
>  #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 */
Not very specific.  Concurrent access usually fine at granularity of
individual read/write as the bus locks protect it.  What state
is actually being protected?  A shared buffer or some state that we
need to ensure remains consistent between driver and 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)
>