git.sh: allow patching submodules

for single-tree project (e.g. flashprog):
config/submodule/PROJECT/MODNAME/patches

for multi-tree project (e.g. coreboot):
config/submodule/PROJECT/TREE/MODNAME/patches

MODNAME is e.g.:
3rdparty/vboot directory in coreboot: would become vboot
(the submodule codepath is filtered to up to the final slash)

another example:
submodire src dir 3rdparty/foo/bar
MODNAME would be "bar"

Add whatever patches you like to a given submodule.

An example patch is included in this commit.

Signed-off-by: Leah Rowe <leah@libreboot.org>

config/submodule/coreboot/default/vboot/patches/0001-test-patch.patch

@@ -0,0 +1,26 @@
+From 68f99140dda455a4f4e9d73df6d7b0a504494e95 Mon Sep 17 00:00:00 2001
+From: Leah Rowe <info@minifree.org>
+Date: Sun, 19 May 2024 23:35:52 +0100
+Subject: [PATCH 1/1] test patch
+
+Signed-off-by: Leah Rowe <info@minifree.org>
+---
+ Makefile | 2 ++
+ 1 file changed, 2 insertions(+)
+
+diff --git a/Makefile b/Makefile
+index 4cb265b2..ef29489f 100644
+--- a/Makefile
++++ b/Makefile
+@@ -2,6 +2,8 @@
+ # Use of this source code is governed by a BSD-style license that can be
+ # found in the LICENSE file.
+ 
++# test
++
+ # This Makefile normally builds in a 'build' subdir, but use
+ #
+ #    make BUILD=<dir>
+-- 
+2.39.2
+

include/git.sh

@@ -93,6 +93,9 @@ git_prep()
 	if [ "$project" != "coreboot" ] || [ $# -gt 2 ]; then
 		[ ! -f "$tmpgit/.gitmodules" ] || git -C "$tmpgit" submodule \
 		    update --init --checkout || $err "git_prep $_loc: !submod"
+
+		patch_submodules
+
 		if [ "$project" = "coreboot" ] && [ -n "$xtree" ] && \
 		    [ "$xtree" != "$tree" ]; then
 			(
@@ -114,6 +117,24 @@ git_prep()
 		x_ ./update project trees -f coreboot "$xtree"; return 0
 }
 
+patch_submodules()
+{
+	moddir="${PWD}/config/submodule/$project"
+	[ -n "$tree" ] && moddir="$moddir/$tree"
+	[ -d "$moddir" ] || return 0
+
+	git -C "$tmpgit" submodule status | awk '{print $2}' > \
+	    "$tmpdir/modules" || $err "$moddir: cannot list submodules"
+
+	while read -r modsrcdir; do
+		modname="${modsrcdir##*/}"
+		modpatchdir="$moddir/$modname/patches"
+		[ -d "$modpatchdir" ] || continue
+
+		git_am_patches "$tmpgit/$modsrcdir" "$modpatchdir"
+	done < "$tmpdir/modules"
+}
+
 git_am_patches()
 {
 	for _patch in "$2/"*; do