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Date:   Tue, 18 May 2021 18:46:07 +0100
From:   Jonathan Cameron <jic23@kernel.org>
To:     Meng.Li@windriver.com
Cc:     lars@metafoo.de, Michael.Hennerich@analog.com, pmeerw@pmeerw.net,
        u.kleine-koenig@pengutronix.de, linux-kernel@vger.kernel.org,
        linux-iio@vger.kernel.org
Subject: Re: [PATCH] driver: adc: ltc2497: return directly after reading the
 adc conversion value
Message-ID: <20210518184607.45b8ccb5@jic23-huawei>
In-Reply-To: <20210512045725.23390-1-Meng.Li@windriver.com>
References: <20210512045725.23390-1-Meng.Li@windriver.com>
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On Wed, 12 May 2021 12:57:25 +0800
Meng.Li@windriver.com wrote:

> From: Meng Li <Meng.Li@windriver.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.
> 
> Fixes: 69548b7c2c4f ("iio: adc: ltc2497: split protocol independent part in a separate module ")
> Cc: stable@vger.kernel.org
> Signed-off-by: Meng Li <Meng.Li@windriver.com>

@Uwe,  I'm far from sure looking at the code what the intent is here.
whilst it definitely changed as Meng Li has outlined, I'm not sure
the fix is correct.

Jonathan

> ---
>  drivers/iio/adc/ltc2497.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> 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,