[PATCH v3 08/12] rockchip: tools: add comment section to rksd.c

[Johan Jonker <jbx6244@gmail.com>]

README.rockchip must be removed.
Move the rksd comment section to rksd.c

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
---
 tools/rksd.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/tools/rksd.c b/tools/rksd.c
index 7d46a1b07b3a..ea12b9cac12e 100644
--- a/tools/rksd.c
+++ b/tools/rksd.c
@@ -3,7 +3,26 @@
  * (C) Copyright 2015 Google,  Inc
  * Written by Simon Glass <sjg@chromium.org>
  *
- * See README.rockchip for details of the rksd format
+ * rksd.c produces an image consisting of 32KB of empty space, a header and
+ * u-boot-spl-dtb.bin. The header is defined by 'struct header0_info' although
+ * most of the fields are unused by U-Boot. We just need to specify the
+ * signature, a flag and the block offset and size of the SPL image.
+ *
+ * The header occupies a single block but we pad it out to 4 blocks. The header
+ * is encoding using RC4 with the key 7c4e0304550509072d2c7b38170d1711. The SPL
+ * image can be encoded too but we don't do that.
+ *
+ * The maximum size of u-boot-spl-dtb.bin which the boot ROM will read is 32KB,
+ * or 0x40 blocks. This is a severe and annoying limitation. There may be a way
+ * around this limitation, since there is plenty of SRAM, but at present the
+ * board refuses to boot if this limit is exceeded.
+ *
+ * The image produced is padded up to a block boundary (512 bytes). It should be
+ * written to the start of an SD card using dd.
+ *
+ * Since this image is set to load U-Boot from the SD card at block offset,
+ * CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR, dd should be used to write
+ * u-boot-dtb.img to the SD card at that offset.
  */

 #include "imagetool.h"
--
2.39.5