Re: [PATCH] hwmon: (da9052) Synchronize access with mfd

[Guenter Roeck <linux@roeck-us.net>]

On 3/18/19 7:29 AM, Samu Nuutamo wrote:
> When tsi-as-adc is configured it is possible for in7[0123]_input read to

in{70,71,72,73}_input ?

> return an incorrect value if a concurrent read to in[456]_input is
> performed. This is likely caused by a concurrent manipulation of the mux
> channel without proper locking as hwmon and mfd use different locks for
> synchronization.
> 
> Switch hwmon to use the same lock as mfd when accessing the TSI channel.
> 
> Fixes: 4f16cab19a3d5 ("hwmon: da9052: Add support for TSI channel")
> Signed-off-by: Samu Nuutamo <samu.nuutamo@vincit.fi>
> ---
>   drivers/hwmon/da9052-hwmon.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/hwmon/da9052-hwmon.c b/drivers/hwmon/da9052-hwmon.c
> index 8ec5bf4ce392..af136a638065 100644
> --- a/drivers/hwmon/da9052-hwmon.c
> +++ b/drivers/hwmon/da9052-hwmon.c
> @@ -249,9 +249,9 @@ static ssize_t da9052_tsi_show(struct device *dev,
>   	int channel = to_sensor_dev_attr(devattr)->index;
>   	int ret;
>   
> -	mutex_lock(&hwmon->hwmon_lock);
> +	mutex_lock(&hwmon->da9052->auxadc_lock);

This is, at best, a kludge.

The hwmon driver doesn't own struct da9052 and should not really access any of its
structure members. The problem suggests that __da9052_read_tsi() should have
been implemented in the mfd core, similar to da9052_adc_manual_read().

Guenter

>   	ret = __da9052_read_tsi(dev, channel);
> -	mutex_unlock(&hwmon->hwmon_lock);
> +	mutex_unlock(&hwmon->da9052->auxadc_lock);
>   
>   	if (ret < 0)
>   		return ret;
>