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

[Jagan Teki]

On Wed, May 29, 2013 at 11:40 AM, Rajeshwari Shinde
<rajeshwari.s at samsung.com> 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 at chromium.org>
> Signed-off-by: Rajeshwari Shinde <rajeshwari.s at 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

I think this 0xec is a value of rx_data what does it indicates and
does this value specific to hw?

--
Thanks,
Jagan.