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

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Message-ID: <ac0a8ff6-92f5-09ef-932b-aba6378f1f47@gmail.com>
Date:   Thu, 24 Jan 2019 20:30:30 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     justinpopo6@...il.com, linux-iio@...r.kernel.org
Cc:     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


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?

> 
> 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?

>  	st->scan_single_xfer[2].rx_buf = &st->single_rx;
>  	st->scan_single_xfer[2].len = 2;
>  
> 

-- 
Florian