Re: [PATCH v8 1/8] iio: dac: ad5696: properly check i2c_transfer() return value

On Thu, 16 Jul 2026 13:14:17 +0100
Rodrigo Alencar via B4 Relay <[email protected]> wrote:

> From: Rodrigo Alencar <[email protected]>
> 
> Verify that the expected number of i2c messages were transferred when
> ad5686_i2c_read() is called. This issue exists since the support for I2C
> devices was first introduced.
> 
> Fixes: 4177381b4401 ("iio:dac:ad5686: Add AD5671R/75R/94/94R/95R/96/96R support")
> Reported-by: [email protected]
> Closes: https://lore.kernel.org/all/[email protected]/
> Reviewed-by: David Lechner <[email protected]>
> Signed-off-by: Rodrigo Alencar <[email protected]>

Let's hold off on this for now.  Whilst it is technically correct today I'm
looking into ensuring that we never need this.  The only error case
today is actually returning 0 which in practice is an error.

> ---
>  drivers/iio/dac/ad5696-i2c.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/dac/ad5696-i2c.c b/drivers/iio/dac/ad5696-i2c.c
> index 279309329b64..551b200bfe14 100644
> --- a/drivers/iio/dac/ad5696-i2c.c
> +++ b/drivers/iio/dac/ad5696-i2c.c
> @@ -7,6 +7,7 @@
>   * Copyright 2018 Analog Devices Inc.
>   */
>  
> +#include <linux/array_size.h>
>  #include <linux/errno.h>
>  #include <linux/i2c.h>
>  #include <linux/mod_devicetable.h>
> @@ -39,9 +40,11 @@ static int ad5686_i2c_read(struct ad5686_state *st, u8 addr)
>  				      AD5686_ADDR(addr) |
>  				      0x00);
>  
> -	ret = i2c_transfer(i2c->adapter, msg, 2);
> +	ret = i2c_transfer(i2c->adapter, msg, ARRAY_SIZE(msg));
>  	if (ret < 0)
>  		return ret;
> +	if (ret != ARRAY_SIZE(msg))
> +		return -EIO;
>  
>  	return be16_to_cpu(st->data[0].d16);
>  }
>