sunxi: (mksunxiboot) signature to indicate "sunxi" SPL variant

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>
Acked-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

diff --git a/arch/arm/include/asm/arch-sunxi/spl.h b/arch/arm/include/asm/arch-sunxi/spl.h
index 5bcd0ebbd03f145fbc20a9a37f0ac550e37c4b97..d2ce8484552d4789ea64ec508ab12922361baee6 100644 (file)
--- a/arch/arm/include/asm/arch-sunxi/spl.h
+++ b/arch/arm/include/asm/arch-sunxi/spl.h
@@ -9,6 +9,8 @@
 #define        _ASM_ARCH_SPL_H_
 
 #define BOOT0_MAGIC            "eGON.BT0"
+#define SPL_SIGNATURE          "SPL" /* marks "sunxi" SPL header */
+#define SPL_HEADER_VERSION     1
 
 /* boot head definition from sun4i boot code */
 struct boot_file_head {
@@ -21,8 +23,23 @@ 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 */
 };
 
 #endif

diff --git a/tools/mksunxiboot.c b/tools/mksunxiboot.c
index 54f4d0564ea5877167164b04d0eaa802f2ceae25..9c1c5b7cee2895d7fb8aa1e79822f0c9452bed8b 100644 (file)
--- a/tools/mksunxiboot.c
+++ b/tools/mksunxiboot.c
@@ -118,6 +118,10 @@ 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));