linux-kernel - Re: [PATCH] hwmon: (ad7314) Validate leading zero bit and return error

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Message-ID: <7f299e75-a4c5-45c8-a755-e0365f8c7e2e@roeck-us.net>
Date: Thu, 20 Feb 2025 14:22:29 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Erik Schumacher <erik.schumacher@...s-sensing.com>
Cc: "linux-hwmon@...r.kernel.org" <linux-hwmon@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"jdelvare@...e.com" <jdelvare@...e.com>
Subject: Re: [PATCH] hwmon: (ad7314) Validate leading zero bit and return
 error

On Thu, Feb 20, 2025 at 10:18:17AM +0000, Erik Schumacher wrote:
> A leading zero bit is sent on the bus before the temperature value is
> transmitted. If this bit is high, the connection might be unstable or it
> could mean that no AD7314 (or compatible) is connected on the bus.
> Return -ENXIO in that case.
> 
> Signed-off-by: Erik Schumacher <erik.schumacher@...s-sensing.com>
> ---
>  drivers/hwmon/ad7314.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/hwmon/ad7314.c b/drivers/hwmon/ad7314.c
> index 7802bbf5f958..025846f1f18b 100644
> --- a/drivers/hwmon/ad7314.c
> +++ b/drivers/hwmon/ad7314.c
> @@ -65,6 +65,10 @@ static ssize_t ad7314_temperature_show(struct device *dev,
>  		return ret;
>  	switch (spi_get_device_id(chip->spi_dev)->driver_data) {
>  	case ad7314:
> +		if (ret & BIT(15)) {
> +			/* Invalid read-out, leading zero bit is missing */
> +			return -ENXIO;

ENXIO = No such device or address

We don't know if that is the case. -EIO seems more appropriate.

Also, AD7301 and AD7302 transmit two leading zeros. If we make this change
for one of the chips supported by the driver, we should make it for all
chips.

Thanks,
Guenter