Re: [PATCH 2/3] spi: bitbang: add lsb first support

[Gerhard Sittig <gsi@xxxxxxx>]

On Wed, Mar 12, 2014 at 16:20 +0100, Michael Grzeschik wrote:
> 
> The bitbang spi driver currently only supports the MSB mode. This patch
> adds the possibility to clock the data in LSB mode.
> 
> Signed-off-by: Michael Grzeschik <m.grzeschik@xxxxxxxxxxxxxx>
> ---
>  drivers/spi/spi-bitbang-txrx.h | 98 +++++++++++++++++++++++++++++-------------
>  drivers/spi/spi-bitbang.c      |  3 +-
>  2 files changed, 71 insertions(+), 30 deletions(-)
> 
> diff --git a/drivers/spi/spi-bitbang-txrx.h b/drivers/spi/spi-bitbang-txrx.h
> index b6e348d..7f9c020 100644
> --- a/drivers/spi/spi-bitbang-txrx.h
> +++ b/drivers/spi/spi-bitbang-txrx.h
> @@ -49,22 +49,42 @@ bitbang_txrx_be_cpha0(struct spi_device *spi,
>  {
>  	/* if (cpol == 0) this is SPI_MODE_0; else this is SPI_MODE_2 */
>  
> -	/* clock starts at inactive polarity */
> -	for (word <<= (32 - bits); likely(bits); bits--) {
> -
> -		/* setup MSB (to slave) on trailing edge */
> -		if ((flags & SPI_MASTER_NO_TX) == 0)
> -			setmosi(spi, word & (1 << 31));
> -		spidelay(nsecs);	/* T(setup) */
> -
> -		setsck(spi, !cpol);
> -		spidelay(nsecs);
> -
> -		/* sample MSB (from slave) on leading edge */
> -		if ((flags & SPI_MASTER_NO_RX) == 0)
> -			word |= getmiso(spi);
> -		setsck(spi, cpol);
> -		word <<= 1;
> +	if (spi->mode & SPI_LSB_FIRST) {
> +		/* clock starts at inactive polarity */
> +		for (; likely(bits); bits--) {
> +
> +			/* setup MSB (to slave) on trailing edge */
> +			if ((flags & SPI_MASTER_NO_TX) == 0)
> +				setmosi(spi, word & 1);
> +			spidelay(nsecs);	/* T(setup) */
> +
> +			setsck(spi, !cpol);
> +			spidelay(nsecs);
> +
> +			/* sample LSB (from slave) on leading edge */
> +			if ((flags & SPI_MASTER_NO_RX) == 0)
> +				word |= getmiso(spi);
> +			setsck(spi, cpol);
> +			word >>= 1;
> +		}
> +	} else {
> +		/* clock starts at inactive polarity */
> +		for (word <<= (32 - bits); likely(bits); bits--) {
> +
> +			/* setup MSB (to slave) on trailing edge */
> +			if ((flags & SPI_MASTER_NO_TX) == 0)
> +				setmosi(spi, word & (1 << 31));
> +			spidelay(nsecs);        /* T(setup) */
> +
> +			setsck(spi, !cpol);
> +			spidelay(nsecs);
> +
> +			/* sample MSB (from slave) on leading edge */
> +			if ((flags & SPI_MASTER_NO_RX) == 0)
> +				word |= getmiso(spi);
> +			setsck(spi, cpol);
> +			word <<= 1;
> +		}
>  	}
>  	return word;
>  }

Would it be useful to not duplicate the transmission logic, but
instead to optionally "bit swap" the TX and RX data before and
after the common transmission logic?  Just a though whether this
might help maintenance.  There might even be existing and proven
code to bit swap integers?


virtually yours
Gerhard Sittig
-- 
DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr. 5, D-82194 Groebenzell, Germany
Phone: +49-8142-66989-0 Fax: +49-8142-66989-80  Email: office@xxxxxxx
--
To unsubscribe from this list: send the line "unsubscribe linux-spi" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html