[U-Boot] [U-Boot,1/2,V5] spi: Add support for preamble bytes

[Jagan Teki <jagannadh.teki@gmail.com>]

On 29-05-2013 01:40, Rajeshwari Shinde wrote:
> A SPI slave may take time to react to a request. For SPI flash devices
> this time is defined as one bit time, or a whole byte for 'fast read'
> mode.
>
> If the SPI slave is another CPU, then the time it takes to react may
> vary. It is convenient to allow the slave device to tag the start of
> the actual reply so that the host can determine when this 'preamble'
> finishes and the actual message starts.
>
> Add a preamble flag to the available SPI flags. If supported by the
> driver then it will ignore any received bytes before the preamble
> on each transaction. This ensures that reliable communication with
> the slave is possible.
>
> Signed-off-by: Simon Glass <sjg@chromium.org>
> Signed-off-by: Rajeshwari Shinde <rajeshwari.s@samsung.com>
>
> ---
> Changes in V2:
> 	- None
> Changes in V3:
> 	- None.
> Changes in V4:
> 	- None.
> Changes in V5:
> 	- In commit message header changed SPI to spi.
>   include/spi.h |    5 +++++
>   1 files changed, 5 insertions(+), 0 deletions(-)
>
> diff --git a/include/spi.h b/include/spi.h
> index 3fe2e1e..1638b50 100644
> --- a/include/spi.h
> +++ b/include/spi.h
> @@ -37,11 +37,16 @@
>   #define	SPI_LSB_FIRST	0x08			/* per-word bits-on-wire */
>   #define	SPI_3WIRE	0x10			/* SI/SO signals shared */
>   #define	SPI_LOOP	0x20			/* loopback mode */
> +#define	SPI_SLAVE	0x40			/* slave mode */
> +#define	SPI_PREAMBLE	0x80			/* Skip preamble bytes */
>   
>   /* SPI transfer flags */
>   #define SPI_XFER_BEGIN	0x01			/* Assert CS before transfer */
>   #define SPI_XFER_END	0x02			/* Deassert CS after transfer */
>   
> +/* Header byte that marks the start of the message */
> +#define SPI_PREAMBLE_END_BYTE	0xec
> +
>   /*-----------------------------------------------------------------------
>    * Representation of a SPI slave, i.e. what we're communicating with.
>    *
Reviewed-by: Jagannadha Sutradharudu Teki <jagannadh.teki@gmail.com>

--
Thanks,
Jagan.