cpu/allwinner/a10: Clarify the usage of SRAM during bootblock

We have 32KiB of usable SRAM right when we boot. The first 24KiB can
be loaded with our bootblock, while the other 8KiB can be used as
stack during the bootblock stage.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Change-Id: I48d3a37869031c3c1dbc1fab71204d473d64deeb
Reviewed-on: http://review.coreboot.org/4563
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

1 files changed, 8 insertions, 7 deletions

diff --git a/src/cpu/allwinner/a10/Makefile.inc b/src/cpu/allwinner/a10/Makefile.inc
index 48f3110605..9f7208ae26 100644
--- a/src/cpu/allwinner/a10/Makefile.inc
+++ b/src/cpu/allwinner/a10/Makefile.inc
@@ -21,15 +21,16 @@ get_bootblock_size= \
 					sed 's/[^0-9 ]//g')) \
 	$(shell echo $$(($(word 2, $(strip $(bb_s))))))
 
-# The boot ROM in the SoC will start loading code if a special boot0 header is
+# The boot ROM in the SoC will start loading code if a special BOOT0 header is
 # found (at an offset of 8KiB in either NAND or SD), and the checksum is
-# correct. this header is normally added by the 'mxsunxiboot' tool. The file
-# passed to mksunxiboot should only include the bootblock due to size
-# limitations.
-# FIXME: Figure out how to safely integrate in coreboot.rom. For now, only copy
-# the first 15 KiB of coreboot.rom (This will not collide with stack)
+# correct. This header is normally added by the 'mxsunxiboot' tool. The boot ROM
+# will load at most 24KiB of data to SRAM, so limit the file size accordingly.
+# The BOOT0 header takes 32 bytes, so limit our file to 24KiB - 32 bytes.
+# FIXME: Figure out how to safely integrate in coreboot.rom.
+# FIXME: The file passed to mksunxiboot should only include the bootblock due
+#	 to size limitations.
 $(obj)/BOOT0: $(obj)/coreboot.rom
 	@printf "    BOOT0      $(subst $(obj)/,,$(^))\n"
 	touch $@
-	dd if=$^ of=$^.tmp bs=1024 count=15
+	dd if=$^ of=$^.tmp bs=24544 count=1
 	-mksunxiboot $^.tmp $@