linux-kernel - Re: [PATCH v2 1/2] hwmon: (sht4x) Fix EREMOTEIO errors

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Message-ID: <f25f8dce-2b65-e98a-349d-220f79473ee2@roeck-us.net>
Date:   Sat, 20 Nov 2021 13:08:12 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     David Mosberger-Tang <davidm@...uge.net>,
        Navin Sankar Velliangiri <navin@...umiz.com>
Cc:     Jean Delvare <jdelvare@...e.com>, linux-hwmon@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] hwmon: (sht4x) Fix EREMOTEIO errors

On 11/20/21 12:40 PM, David Mosberger-Tang wrote:
> Per datasheet, SHT4x may need up to 8.2ms for a "high repeatability"
> measurement to complete.  Attempting to read the result too early
> triggers a NAK which then causes an EREMOTEIO error.
> 
> This behavior has been confirmed with a logic analyzer while running
> the I2C bus at only 40kHz.  The low frequency precludes any
> signal-integrity issues, which was also confirmed by the absence of
> any CRC8 errors.  In this configuration, a NAK occurred on any read
> that followed the measurement command within less than 8.2ms.
> 
> Signed-off-by: David Mosberger-Tang <davidm@...uge.net>

You sent v2 after 5 minutes, and there is no change log.
Please never do that, and always provide a change log.

Guenter

> ---
>   drivers/hwmon/sht4x.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/hwmon/sht4x.c b/drivers/hwmon/sht4x.c
> index 09c2a0b06444..3415d7a0e0fc 100644
> --- a/drivers/hwmon/sht4x.c
> +++ b/drivers/hwmon/sht4x.c
> @@ -23,7 +23,7 @@
>   /*
>    * I2C command delays (in microseconds)
>    */
> -#define SHT4X_MEAS_DELAY	1000
> +#define SHT4X_MEAS_DELAY_HPM	8200	/* see t_MEAS,h in datasheet */
>   #define SHT4X_DELAY_EXTRA	10000
>   
>   /*
> @@ -90,7 +90,7 @@ static int sht4x_read_values(struct sht4x_data *data)
>   	if (ret < 0)
>   		goto unlock;
>   
> -	usleep_range(SHT4X_MEAS_DELAY, SHT4X_MEAS_DELAY + SHT4X_DELAY_EXTRA);
> +	usleep_range(SHT4X_MEAS_DELAY_HPM, SHT4X_MEAS_DELAY_HPM + SHT4X_DELAY_EXTRA);
>   
>   	ret = i2c_master_recv(client, raw_data, SHT4X_RESPONSE_LENGTH);
>   	if (ret != SHT4X_RESPONSE_LENGTH) {
>