README: document CONFIG_ENV_IS_IN_SPI_FLASH

The option can be used to save the environment in spi flash.
Implementation code is already exist in command/env_sf.c. But
the documentation is missing.

This patch add the details for this option to the README file.

Signed-off-by: Josh Wu <josh.wu@atmel.com>
Reviewed-by: Jagannadha Sutradharudu Teki <jaganna@xilinx.com>

diff --git a/README b/README
index 0c98545a0d174e6fd0daeed9d11d08de2dd620a6..2bc0d3560c7735d87d38df157d03005700b75bd0 100644 (file)
--- a/README
+++ b/README
@@ -4069,6 +4069,43 @@ to save the current settings.
          environment area within the total memory of your DataFlash placed
          at the specified address.
 
+- CONFIG_ENV_IS_IN_SPI_FLASH:
+
+       Define this if you have a SPI Flash memory device which you
+       want to use for the environment.
+
+       - CONFIG_ENV_OFFSET:
+       - CONFIG_ENV_SIZE:
+
+         These two #defines specify the offset and size of the
+         environment area within the SPI Flash. CONFIG_ENV_OFFSET must be
+         aligned to an erase sector boundary.
+
+       - CONFIG_ENV_SECT_SIZE:
+
+         Define the SPI flash's sector size.
+
+       - CONFIG_ENV_OFFSET_REDUND (optional):
+
+         This setting describes a second storage area of CONFIG_ENV_SIZE
+         size used to hold a redundant copy of the environment data, so
+         that there is a valid backup copy in case there is a power failure
+         during a "saveenv" operation. CONFIG_ENV_OFFSET_RENDUND must be
+         aligned to an erase sector boundary.
+
+       - CONFIG_ENV_SPI_BUS (optional):
+       - CONFIG_ENV_SPI_CS (optional):
+
+         Define the SPI bus and chip select. If not defined they will be 0.
+
+       - CONFIG_ENV_SPI_MAX_HZ (optional):
+
+         Define the SPI max work clock. If not defined then use 1MHz.
+
+       - CONFIG_ENV_SPI_MODE (optional):
+
+         Define the SPI work mode. If not defined then use SPI_MODE_3.
+
 - CONFIG_ENV_IS_IN_REMOTE:
 
        Define this if you have a remote memory space which you