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

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Date:   Mon, 24 May 2021 02:53:36 +0000
From:   "Li, Meng" <Meng.Li@...driver.com>
To:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
CC:     "lars@...afoo.de" <lars@...afoo.de>,
        "Michael.Hennerich@...log.com" <Michael.Hennerich@...log.com>,
        "jic23@...nel.org" <jic23@...nel.org>,
        "pmeerw@...erw.net" <pmeerw@...erw.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>
Subject: RE: [PATCH] driver: adc: ltc2497: return directly after reading the
 adc conversion value



> -----Original Message-----
> From: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> Sent: Wednesday, May 19, 2021 5:21 PM
> To: Li, Meng <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.
> 

Hi Uwe,

Thanks for your comments.
I would like to verify your ideal if you can offer your patch or tell me where to change code.

Thanks,
Limeng


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