linux-kernel - Re: [PATCH] driver: adc: ltc2497: return directly after reading the adc conversion value

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Message-ID: <20210603172025.314b5ced@jic23-huawei>
Date:   Thu, 3 Jun 2021 17:20:25 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Meng.Li@...driver.com
Cc:     lars@...afoo.de, Michael.Hennerich@...log.com, pmeerw@...erw.net,
        u.kleine-koenig@...gutronix.de, linux-kernel@...r.kernel.org,
        linux-iio@...r.kernel.org
Subject: Re: [PATCH] driver: adc: ltc2497: return directly after reading the
 adc conversion value

On Tue,  1 Jun 2021 17:28:05 +0800
Meng.Li@...driver.com wrote:

> From: Meng Li <Meng.Li@...driver.com>
> 
> When read adc conversion value with below command:
> cat /sys/.../iio:device0/in_voltage0-voltage1_raw
> There is an error reported as below:
> ltc2497 0-0014: i2c transfer failed: -EREMOTEIO
> This i2c transfer issue is introduced by commit 69548b7c2c4f ("iio:
> adc: ltc2497: split protocol independent part in a separate module").
> When extract the common code into ltc2497-core.c, it change the
> code logic of function ltc2497core_read(). With wrong reading
> sequence, the action of enable adc channel is sent to chip again
> during adc channel is in conversion status. In this way, there is
> no ack from chip, and then cause i2c transfer failed.
> In order to keep the code logic is the same with original ideal,
> it is need to return direct after reading the adc conversion value.
> 
> v2:
> According to ltc2497 datasheet, the max value of conversion time is
> 149.9 ms. So, add 20% to the 150msecs so that there is enough time
> for data conversion.

Version change logs go below the --- as we don't want to preserve them
forever in the git history.

I may have lost track of the discussion, but I thought the idea was that perhaps
the longer time period would remove the need for the early return?

Thanks,

Jonathan
> 
> Fixes: 69548b7c2c4f ("iio: adc: ltc2497: split protocol independent part in a separate module ")
> Cc: stable@...r.kernel.org
> Signed-off-by: Meng Li <Meng.Li@...driver.com>
> ---
>  drivers/iio/adc/ltc2497.c | 2 ++
>  drivers/iio/adc/ltc2497.h | 2 +-
>  2 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/adc/ltc2497.c b/drivers/iio/adc/ltc2497.c
> index 1adddf5a88a9..fd5a66860a47 100644
> --- a/drivers/iio/adc/ltc2497.c
> +++ b/drivers/iio/adc/ltc2497.c
> @@ -41,6 +41,8 @@ static int ltc2497_result_and_measure(struct ltc2497core_driverdata *ddata,
>  		}
>  
>  		*val = (be32_to_cpu(st->buf) >> 14) - (1 << 17);
> +
> +		return ret;
>  	}
>  
>  	ret = i2c_smbus_write_byte(st->client,
> diff --git a/drivers/iio/adc/ltc2497.h b/drivers/iio/adc/ltc2497.h
> index d0b42dd6b8ad..e451930837d8 100644
> --- a/drivers/iio/adc/ltc2497.h
> +++ b/drivers/iio/adc/ltc2497.h
> @@ -2,7 +2,7 @@
>  
>  #define LTC2497_ENABLE			0xA0
>  #define LTC2497_CONFIG_DEFAULT		LTC2497_ENABLE
> -#define LTC2497_CONVERSION_TIME_MS	150ULL
> +#define LTC2497_CONVERSION_TIME_MS	180ULL
>  
>  struct ltc2497core_driverdata {
>  	struct regulator *ref;