linux-kernel - Re: [PATCH] staging: iio: ad2s1210: Fix SPI reading

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Message-ID: <20200503123753.29ea8be0@archlinux>
Date:   Sun, 3 May 2020 12:37:53 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Alexandru Ardelean <alexandru.ardelean@...log.com>
Cc:     <linux-iio@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <devel@...verdev.osuosl.org>, <gregkh@...uxfoundation.org>,
        Dragos Bogdan <dragos.bogdan@...log.com>
Subject: Re: [PATCH] staging: iio: ad2s1210: Fix SPI reading

On Wed, 29 Apr 2020 10:21:29 +0300
Alexandru Ardelean <alexandru.ardelean@...log.com> wrote:

> From: Dragos Bogdan <dragos.bogdan@...log.com>
> 
> If the serial interface is used, the 8-bit address should be latched using
> the rising edge of the WR/FSYNC signal.
> 
> This basically means that a CS change is required between the first byte
> sent, and the second one.
> This change splits the single-transfer transfer of 2 bytes into 2 transfers
> with a single byte, and CS change in-between.
> 
> Signed-off-by: Dragos Bogdan <dragos.bogdan@...log.com>
> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@...log.com>

Fixes tag would have been nice. I've had a go by picking a patch where I
refactored this code, but I think the issue probably predates that one.
Its in 2011 so I doubt anyone will try going past that with backports ;)

Applied to the fixes-togreg branch of iio.git and marked for stable.

I'm guessing this means you have hardware and hope to get this one out
of staging shortly? *crosses fingers* :)

Jonathan

> ---
>  drivers/staging/iio/resolver/ad2s1210.c | 17 ++++++++++++-----
>  1 file changed, 12 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/staging/iio/resolver/ad2s1210.c b/drivers/staging/iio/resolver/ad2s1210.c
> index 4b25a3a314ed..ed404355ea4c 100644
> --- a/drivers/staging/iio/resolver/ad2s1210.c
> +++ b/drivers/staging/iio/resolver/ad2s1210.c
> @@ -130,17 +130,24 @@ static int ad2s1210_config_write(struct ad2s1210_state *st, u8 data)
>  static int ad2s1210_config_read(struct ad2s1210_state *st,
>  				unsigned char address)
>  {
> -	struct spi_transfer xfer = {
> -		.len = 2,
> -		.rx_buf = st->rx,
> -		.tx_buf = st->tx,
> +	struct spi_transfer xfers[] = {
> +		{
> +			.len = 1,
> +			.rx_buf = &st->rx[0],
> +			.tx_buf = &st->tx[0],
> +			.cs_change = 1,
> +		}, {
> +			.len = 1,
> +			.rx_buf = &st->rx[1],
> +			.tx_buf = &st->tx[1],
> +		},
>  	};
>  	int ret = 0;
>  
>  	ad2s1210_set_mode(MOD_CONFIG, st);
>  	st->tx[0] = address | AD2S1210_MSB_IS_HIGH;
>  	st->tx[1] = AD2S1210_REG_FAULT;
> -	ret = spi_sync_transfer(st->sdev, &xfer, 1);
> +	ret = spi_sync_transfer(st->sdev, xfers, 2);
>  	if (ret < 0)
>  		return ret;
>