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

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Date:   Wed, 19 May 2021 11:21:04 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Meng.Li@...driver.com
Cc:     lars@...afoo.de, Michael.Hennerich@...log.com, jic23@...nel.org,
        pmeerw@...erw.net, 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 Wed, May 12, 2021 at 12:57:25PM +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.
> 
> 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 ++
>  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;

This looks wrong for me. The idea of the function
ltc2497_result_and_measure is that it reads the result and starts a new
measurement. I guess the problem is that ltc2497_result_and_measure is
called to early, not that it does too much.

But note I don't have such a system handy to actually debug this any
more.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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