Re: [PATCH] i.MX: SPI: Respect SPI_LSB_FIRST flag in mode settings

[Sascha Hauer <s.hauer@pengutronix.de>]

Hi Andrey,

On Wed, Dec 31, 2014 at 07:10:55AM -0800, Andrey Smirnov wrote:
> Add code to support SPI transfers that have data shifted out least
> significant bit first. This is useful in many cases, but specifically
> it is needed for drivers/firmware/altera_serial.c to work on i.MX
> platform.
> 
> Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
> ---
>  drivers/spi/imx_spi.c | 50 ++++++++++++++++++++++++++++++++++++++++++++------
>  1 file changed, 44 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/spi/imx_spi.c b/drivers/spi/imx_spi.c
> index 3146339..efbbb08 100644
> --- a/drivers/spi/imx_spi.c
> +++ b/drivers/spi/imx_spi.c
> @@ -137,6 +137,25 @@ static int imx_spi_setup(struct spi_device *spi)
>  	return 0;
>  }
>  
> +static unsigned int imx_spi_maybe_reverse_bits(struct spi_device *spi, unsigned int word)
> +{
> +	unsigned int result = word;
> +
> +	if (spi->mode & SPI_LSB_FIRST) {
> +		size_t bits_left = spi->bits_per_word - 1;
> +
> +		for (word >>= 1; word; word >>= 1) {
> +			result <<= 1;
> +			result |= word & 1;
> +			bits_left--;
> +		}
> +
> +		result <<= bits_left;
> +	}
> +
> +	return result;
> +}
> +
>  static unsigned int cspi_0_0_xchg_single(struct imx_spi *imx, unsigned int data)
>  {
>  	void __iomem *base = imx->regs;
> @@ -386,6 +405,7 @@ static void imx_spi_do_transfer(struct spi_device *spi, struct spi_transfer *t)
>  {
>  	struct imx_spi *imx = container_of(spi->master, struct imx_spi, master);
>  	unsigned i;
> +	u32 tx_val;
>  
>  	if (spi->bits_per_word <= 8) {
>  		const u8	*tx_buf = t->tx_buf;
> @@ -393,9 +413,15 @@ static void imx_spi_do_transfer(struct spi_device *spi, struct spi_transfer *t)
>  		u8		rx_val;
>  
>  		for (i = 0; i < t->len; i++) {
> -			rx_val = imx->xchg_single(imx, tx_buf ? tx_buf[i] : 0);
> +			if (tx_buf)
> +				tx_val = imx_spi_maybe_reverse_bits(spi, tx_buf[i]);
> +			else
> +				tx_val = 0;
> +
> +			rx_val = imx->xchg_single(imx, tx_val);
> +

Better introduce a imx_xchg_single which does the necessary bit
reversing and calls imx->xchg_single. This avoids duplicating the code
for all three bits_per_word settings.

Sascha

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