linux-kernel - Re: [PATCH] iio: adc: ti-ads7950: inconsistency with spi msg

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Message-ID: <CAJx26kWg=9FQonEWRQ2OjQWEStRQ_p8OOgperFp+9E_UdQGYNQ@mail.gmail.com>
Date:   Thu, 24 Jan 2019 21:56:50 -0800
From:   Justin Chen <justinpopo6@...il.com>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     linux-iio@...r.kernel.org, jic23@...nel.org, knaack.h@....de,
        lars@...afoo.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iio: adc: ti-ads7950: inconsistency with spi msg

Hello Florian


On Thu, Jan 24, 2019 at 8:30 PM Florian Fainelli <f.fainelli@...il.com> wrote:
>
>
> Hi Justin,
>
> On 1/24/19 5:56 PM, justinpopo6@...il.com wrote:
> > From: Justin Chen <justinpopo6@...il.com>
> >
> > To read a channel we require 3 cycles to send, process, and receive
> > the data. The transfer buffer for the third transaction is left blank.
> > This leaves it up to the SPI driver to decide what to do.
> >
> > In one particular case, if the tx buffer is not set the spi driver
> > sets it to 0xff. This puts the ADC in a alarm programming state,
> > therefore the following read to a channel becomes erroneous.
> >
> > Instead of leaving us to the mercy of the SPI driver, we send the
> > ADC cmd on the third transaction to prevent inconsistent behavior.
>
> Do you think this warrants a Fixes: tag?
>
This was an issue when the driver was introduced. Should I tag that
commit the introduced the driver?
> >
> > Signed-off-by: Justin Chen <justinpopo6@...il.com>
> > ---
> >  drivers/iio/adc/ti-ads7950.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/drivers/iio/adc/ti-ads7950.c b/drivers/iio/adc/ti-ads7950.c
> > index 0ad6359..5453e10 100644
> > --- a/drivers/iio/adc/ti-ads7950.c
> > +++ b/drivers/iio/adc/ti-ads7950.c
> > @@ -422,6 +422,7 @@ static int ti_ads7950_probe(struct spi_device *spi)
> >       st->scan_single_xfer[1].tx_buf = &st->single_tx;
> >       st->scan_single_xfer[1].len = 2;
> >       st->scan_single_xfer[1].cs_change = 1;
> > +     st->scan_single_xfer[2].rx_buf = &st->single_tx;
>
> Should this be st->scan_single_xfer[2].tx_buf?
>
Oh yes. Good catch. Careless mistake! v2 incoming.
> >       st->scan_single_xfer[2].rx_buf = &st->single_rx;
> >       st->scan_single_xfer[2].len = 2;
> >
> >
>
> --
> Florian