[PATCH v2] mx8m: csf.sh: pad csf blob for u-boot.itb to CSF_SIZE minus IVT header

[Rasmus Villemoes]

When built with CONFIG_IMX_HAB, the full FIT image, including stuff
tacked on beyond the end of the fdt structure, is expected to be (fdt
size rounded up to 0x1000 boundary)+CONFIG_CSF_SIZE.

Now, when the FIT image is loaded from a storage device, it doesn't
really matter that the flash.bin that gets written to target isn't
quite that big - we will just load some garbage bytes that are never
read or used for anything. But when flash.bin is uploaded via uuu,
it's important that we actually serve at least as many bytes as the
target expects, or we will hang in rom_api_download_image().

Extend the logic in the csf.sh script so that the csf blob is padded
to CONFIG_CSF_SIZE minus the size of the IVT header.

Signed-off-by: Rasmus Villemoes <rasmus.villemoes at prevas.dk>
---
v2: use dd instead of truncate.

 doc/imx/habv4/csf_examples/mx8m/csf.sh | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/doc/imx/habv4/csf_examples/mx8m/csf.sh b/doc/imx/habv4/csf_examples/mx8m/csf.sh
index 65c143073c..cd3b2614a2 100644
--- a/doc/imx/habv4/csf_examples/mx8m/csf.sh
+++ b/doc/imx/habv4/csf_examples/mx8m/csf.sh
@@ -75,5 +75,18 @@ dd if=ivt.bin of=flash.bin bs=1 seek=${ivt_block_offset} conv=notrunc
 
 # Generate CSF blob
 cst -i csf_fit.tmp -o csf_fit.bin
+
+# When loading flash.bin via USB, we must ensure that the file being
+# served is as large as the target expects (see
+# board_spl_fit_size_align()), otherwise the target will hang in
+# rom_api_download_image() waiting for the remaining bytes.
+#
+# Note that in order for dd to actually extend the file, one must not
+# pass conv=notrunc here. With a non-zero seek= argument, dd is
+# documented to preserve the contents of the file seeked past; in
+# particular, dd does not open the file with O_TRUNC.
+CSF_SIZE=$(sed -n "/CONFIG_CSF_SIZE=/ s at .*=@@p" .config)
+dd if=/dev/null of=csf_fit.bin bs=1 seek=$((CSF_SIZE - 0x20)) count=0
+
 # Patch CSF blob into flash.bin
 dd if=csf_fit.bin of=flash.bin bs=1 seek=${csf_block_offset} conv=notrunc
-- 
2.37.2