linux-kernel - Re: [PATCH 2/2] iio:adc:ti-ads124s08: Fix packet read from the ADC

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Message-ID: <20210124151242.285ce9c6@archlinux>
Date:   Sun, 24 Jan 2021 15:12:42 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Dan Murphy <dmurphy@...com>
Cc:     <linux-iio@...r.kernel.org>, <lars@...afoo.de>,
        <pmeerw@...erw.net>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] iio:adc:ti-ads124s08: Fix packet read from the ADC

On Thu, 21 Jan 2021 13:14:31 -0600
Dan Murphy <dmurphy@...com> wrote:

> Fix the spi_transfer array in the reading of the data from the ADC.
> 
> Fixes: ("e717f8c6dfec iio: adc: Add the TI ads124s08 ADC code")
> Signed-off-by: Dan Murphy <dmurphy@...com>

I'm not really following the changes below..

> ---
>  drivers/iio/adc/ti-ads124s08.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/drivers/iio/adc/ti-ads124s08.c b/drivers/iio/adc/ti-ads124s08.c
> index f05d4e0e1c9d..023d81c7e8da 100644
> --- a/drivers/iio/adc/ti-ads124s08.c
> +++ b/drivers/iio/adc/ti-ads124s08.c
> @@ -201,12 +201,10 @@ static int ads124s_read(struct iio_dev *indio_dev, unsigned int chan)
>  	struct spi_transfer t[] = {
>  		{
>  			.tx_buf = &priv->data[0],
> -			.len = 4,
> -			.cs_change = 1,

We should still need to provide a length for this transfer.

>  		}, {
> -			.tx_buf = &priv->data[1],
>  			.rx_buf = &priv->data[1],
>  			.len = 4,
> +			.cs_change = 1,

That's unusual... cs_change being set on the last transfer means
the opposite of what it does for earlier transfers.

https://elixir.bootlin.com/linux/latest/source/include/linux/spi/spi.h#L905

Or is the intent here to provide a performance hint that the device doesn't
care if the cs line goes inactive before stating a new set of transfers?
If so add a comment to say that perhaps.

>  		},
>  	};
>