Sender: Guenter Roeck <groeck7@gmail.com>
Date:   Sat, 20 Nov 2021 14:45:08 -0800
From:   Guenter Roeck <linux@roeck-us.net>
To:     David Mosberger-Tang <davidm@egauge.net>
Cc:     Navin Sankar Velliangiri <navin@linumiz.com>,
        Jean Delvare <jdelvare@suse.com>, linux-hwmon@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3] hwmon: (sht4x) Fix EREMOTEIO errors
Message-ID: <20211120224508.GA1292983@roeck-us.net>
References: <20211120204053.2299501-1-davidm@egauge.net>
 <20211120212849.2300854-1-davidm@egauge.net>
 <20211120212849.2300854-2-davidm@egauge.net>
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In-Reply-To: <20211120212849.2300854-2-davidm@egauge.net>
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On Sat, Nov 20, 2021 at 09:28:56PM +0000, 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@egauge.net>

Applied.

Thanks,
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) {