Re: [PATCH] hwmon: (lm90) Fix false alarm when writing convrate on max6658

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

On Thu, Mar 04, 2021 at 04:38:32PM +0100, Paul Menzel wrote:
> From: Boyang Yu <byu@arista.com>
> 
> We found that the max6658 sometimes issues a false alarm when its
> convrate is changed, with the current hwmon driver. This workaround
> will fix it by stopping the conversion before setting the convrate.
> 
> Upstream the patch added added to the SONiC Linux kernel in merge/pull
> request #82 [1][2].
> 
> [1]: https://github.com/Azure/sonic-linux-kernel/pull/82
> [2]: https://github.com/Azure/sonic-linux-kernel/commit/d03f6167f64b2bfa1330ff7b33fe217f68ab7028
> 
> [pmenzel: Forward port patch from 4.19 to 5.12-rc1+]
> Signed-off-by: Paul Menzel <pmenzel@molgen.mpg.de>
> ---
>  drivers/hwmon/lm90.c | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/hwmon/lm90.c b/drivers/hwmon/lm90.c
> index ebbfd5f352c0..0c1a91b715e8 100644
> --- a/drivers/hwmon/lm90.c
> +++ b/drivers/hwmon/lm90.c
> @@ -639,7 +639,11 @@ static int lm90_set_convrate(struct i2c_client *client, struct lm90_data *data,
>  		if (interval >= update_interval * 3 / 4)
>  			break;
>  
> -	err = lm90_write_convrate(data, i);
> +	if (data->kind == max6657)
> +		err = max6657_write_convrate(client, i);

There is no such function in the upstream kernel.
Anyway, this problem has already been already fixed
in the upstream kernel with commit 62456189f3292 ("hwmon:
(lm90) Fix max6658 sporadic wrong temperature reading").

Guenter

> +	else
> +		err = lm90_write_convrate(data, i);
> +
>  	data->update_interval = DIV_ROUND_CLOSEST(update_interval, 64);
>  	return err;
>  }
> @@ -1649,7 +1653,11 @@ static void lm90_restore_conf(void *_data)
>  	struct i2c_client *client = data->client;
>  
>  	/* Restore initial configuration */
> -	lm90_write_convrate(data, data->convrate_orig);
> +	if (data->kind == max6657)
> +		max6657_write_convrate(client, data->convrate_orig);
> +	else
> +		lm90_write_convrate(data, data->convrate_orig);
> +
>  	i2c_smbus_write_byte_data(client, LM90_REG_W_CONFIG1,
>  				  data->config_orig);
>  }
> @@ -1672,7 +1680,8 @@ static int lm90_init_client(struct i2c_client *client, struct lm90_data *data)
>  	data->config_orig = config;
>  	data->config = config;
>  
> -	lm90_set_convrate(client, data, 500); /* 500ms; 2Hz conversion rate */
> +	if (data->kind != max6657)
> +		lm90_set_convrate(client, data, 500); /* 500ms; 2Hz conversion rate */
>  
>  	/* Check Temperature Range Select */
>  	if (data->kind == adt7461 || data->kind == tmp451) {