[U-Boot] [PATCH v2 1/3] sunxi: (mksunxiboot) signature to indicate "sunxi" SPL variant

Bernhard Nortmann
2015-09-14T13:15:28Z

This patch follows up on a discussion of ways to improve support
for the sunxi FEL ("USB boot") mechanism, especially with regard
to boot scripts, see:
https://groups.google.com/d/msg/linux-sunxi/wBEGUoLNRro/rHGq6nSYCQAJ

The idea is to convert the (currently unused) "pad" bytes in the
SPL header into an area where data can be passed to U-Boot. To
do this safely, we have to make sure that we're actually using
our "sunxi" flavor of the SPL, and not the Allwinner boot0.

The modified mksunxiboot introduces a special signature to the
SPL header in place of the "pub_head_size" field. This can be
used to reliably distinguish between compatible versions of sunxi
SPL and anything else (older variants or Allwinner's boot0).

Signed-off-by: Bernhard Nortmann <bernhard.nortmann@web.de>
---

Changes in v2:
- Rename field to fel_script_address, discard fel_data_size
- Clearing header fields is no longer needed, as mksunxiboot.c zeroes entire image first

tools/mksunxiboot.c | 23 ++++++++++++++++++++++-
1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/tools/mksunxiboot.c b/tools/mksunxiboot.c
index 676d392..cb0865c 100644
--- a/tools/mksunxiboot.c
+++ b/tools/mksunxiboot.c
@@ -27,12 +27,29 @@ struct boot_file_head {
* by the boot ROM. To be compatible with Allwinner tools we
* would need to implement the proper fields here instead of
* padding.
+ *
+ * Actually we want the ability to recognize our "sunxi" variant
+ * of the SPL. To do so, let's place a special signature into the
+ * "pub_head_size" field. We can reasonably expect Allwinner's
+ * boot0 to always have the upper 16 bits of this set to 0 (after
+ * all the value shouldn't be larger than the limit imposed by
+ * SRAM size).
+ * If the signature is present (at 0x14), then we know it's safe
+ * to use the remaining 8 bytes (at 0x18) for our own purposes.
+ * (E.g. sunxi-tools "fel" utility can pass information there.)
*/
- uint8_t pad[12]; /* align to 32 bytes */
+ union {
+ uint32_t pub_head_size;
+ uint8_t spl_signature[4];
+ };
+ uint32_t fel_script_address;
+ uint32_t reserved; /* padding, align to 32 bytes */
};

#define BOOT0_MAGIC "eGON.BT0"
#define STAMP_VALUE 0x5F0A6C39
+#define SPL_SIGNATURE "SPL" /* marks "sunxi" header */
+#define SPL_HEADER_VERSION 1

/* check sum functon from sun4i boot code */
int gen_check_sum(struct boot_file_head *head_p)
@@ -133,6 +150,10 @@ int main(int argc, char *argv[])
ALIGN(file_size + sizeof(struct boot_file_head), BLOCK_SIZE);
img.header.b_instruction = cpu_to_le32(img.header.b_instruction);
img.header.length = cpu_to_le32(img.header.length);
+
+ memcpy(img.header.spl_signature, SPL_SIGNATURE, 3); /* "sunxi" marker */
+ img.header.spl_signature[3] = SPL_HEADER_VERSION;
+
gen_check_sum(&img.header);

count = write(fd_out, &img, le32_to_cpu(img.header.length));
--
2.4.6