Re: [PATCH] tmp102: Fix first temperature reading

[Jean Delvare <jdelvare@suse.de>]

Hi Guenter,

On Mon, 23 Oct 2017 17:55:26 -0700, Guenter Roeck wrote:
> Commit 3d8f7a89a197 ("hwmon: (tmp102) Improve handling of initial read
> delay") reduced the initial temperature read delay and made it dependent
> on the chip's shutdown mode. If the chip was not in shutdown mode at probe,
> the read delay no longer applies.
> 
> This ignores the fact that the chip initialization changes the temperature
> sensor resolution, and that the temperature register values change when
> the resolution is changed. As a result, the reported temperature is twice
> as high as the real temperature until the first temperature conversion
> after the configuration change is complete. This can result in unexpected
> behavior and, worst case, in a system shutdown. To fix the problem,
> let's just always wait for a conversion to complete before reporting
> a temperature.
> 
> Fixes: 3d8f7a89a197 ("hwmon: (tmp102) Improve handling of initial read delay")
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=197167
> Reported-by: Ralf Goebel <ralf.goebel@imago-technologies.com>
> Cc: Ralf Goebel <ralf.goebel@imago-technologies.com>
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> ---
>  drivers/hwmon/tmp102.c | 9 +--------
>  1 file changed, 1 insertion(+), 8 deletions(-)
> 
> diff --git a/drivers/hwmon/tmp102.c b/drivers/hwmon/tmp102.c
> index 5eafbaada795..1af1932a72db 100644
> --- a/drivers/hwmon/tmp102.c
> +++ b/drivers/hwmon/tmp102.c
> @@ -268,14 +268,7 @@ static int tmp102_probe(struct i2c_client *client,
>  		return err;
>  	}
>  
> -	tmp102->ready_time = jiffies;
> -	if (tmp102->config_orig & TMP102_CONF_SD) {
> -		/*
> -		 * Mark that we are not ready with data until the first
> -		 * conversion is complete
> -		 */
> -		tmp102->ready_time += msecs_to_jiffies(CONVERSION_TIME_MS);
> -	}
> +	tmp102->ready_time = jiffies + msecs_to_jiffies(CONVERSION_TIME_MS);
>  
>  	hwmon_dev = devm_hwmon_device_register_with_info(dev, client->name,
>  							 tmp102,

Thanks for the quick fix. The change itself looks good but why remove
the comment, which I think still retains its value?

Reviewed-by: Jean Delvare <jdelvare@suse.de>

-- 
Jean Delvare
SUSE L3 Support