tests: dt_binding_check: new test

We currently "rely" on Rob Herring's mail bot to provide sanity checking
on patches that touch device tree bindings:
https://lore.kernel.org/netdev/176134124286.2841725.8990137232361008022.robh@kernel.org

and that is sufficient in "public" settings (patches sent to
netdev@vger.kernel.org and devicetree@vger.kernel.org also copied).

But in "private" settings (i.e. individual developers encouraged to do
sanity checking on their own, for example by running ingest_mdir),
something that replicates Rob's mail bot is still required:
https://gitlab.com/robherring/dt-review-ci/
https://gitlab.com/robherring/pw-utils

The justification for including it in NIPA is that while device tree
maintainers review binding patches, they get applied to the subsystem
tree (in this case netdev).

In terms of implementation, "make dt_binding_check" does not always
nicely print "error" or "warning" on the lines with issues. Furthermore,
the errors are multi-line. The "normal" lines contain things such as
"make", "SCHEMA", "CHKDT", "LINT", "DTEX", "DTC" at the beginning.
Instead of detecting all 'normal' lines to filter them out, we just use
'make -s' which suppresses them, and leaves only the error messages.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>

Author: vladimiroltean

tests/patch/dt_binding_check/dt_binding_check.sh

@@ -0,0 +1,81 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright 2025-2026 NXP
+
+HEAD=$(git rev-parse HEAD)
+ncpu=$(grep -c processor /proc/cpuinfo)
+rc=0
+
+pr() {
+    echo " ====== $* ======" | tee -a /dev/stderr
+}
+
+build() {
+    make -s -j $ncpu DT_CHECKER_FLAGS=-m dt_binding_check 2>&1
+}
+
+# Only run this check if the patch touches DT binding files.
+if ! git show --diff-filter=AM --pretty="" --name-only "${HEAD}" | \
+    grep -q -E "^Documentation/devicetree/bindings/"
+then
+    echo "No DT binding files touched, skip" >&"$DESC_FD"
+    exit 0
+fi
+
+# Create temporary files for logs
+tmpfile_o_raw=$(mktemp)
+tmpfile_n_raw=$(mktemp)
+tmp_new_issues=$(mktemp)
+
+echo "Tree base:"
+git log -1 --pretty='%h ("%s")' HEAD~
+echo "Now at:"
+git log -1 --pretty='%h ("%s")' HEAD
+
+pr "Checking before the patch"
+git checkout -q HEAD~
+
+# Run the check on the parent commit
+(build | tee -a "$tmpfile_o_raw") || true
+
+# Sort the output
+sort "$tmpfile_o_raw" > "${tmpfile_o_raw}.sorted"
+mv "${tmpfile_o_raw}.sorted" "$tmpfile_o_raw"
+incumbent_total=$(wc -l < "$tmpfile_o_raw")
+
+pr "Checking the tree with the patch"
+git checkout -q "$HEAD"
+
+# Run the check on the new commit
+(build | tee -a "$tmpfile_n_raw") || true
+
+# Sort the output
+sort "$tmpfile_n_raw" > "${tmpfile_n_raw}.sorted"
+mv "${tmpfile_n_raw}.sorted" "$tmpfile_n_raw"
+current_total=$(wc -l < "$tmpfile_n_raw")
+
+# Compare the lists to find new and fixed issues
+# Use comm to find fixed issues (lines only in the old log, column 1).
+fixed_issues_count=$(comm -23 "$tmpfile_o_raw" "$tmpfile_n_raw" | wc -l)
+
+# Use comm to find new issues (lines only in the new log, column 2)
+# and save them for later display.
+comm -13 "$tmpfile_o_raw" "$tmpfile_n_raw" > "$tmp_new_issues"
+new_issues_count=$(wc -l < "$tmp_new_issues")
+
+echo "Issues before: $incumbent_total, after: $current_total" \
+    "(Fixed: $fixed_issues_count, New: $new_issues_count)" >&"$DESC_FD"
+
+if [ "$new_issues_count" -gt 0 ]; then
+    echo "New issues added:" 1>&2
+    # Print the new issues we saved
+    cat "$tmp_new_issues" 1>&2
+    rc=1
+elif [ "$fixed_issues_count" -gt 0 ]; then
+    echo "Patch fixed $fixed_issues_count issue(s)." >&2
+    # No new issues, and some were fixed. This is a success.
+fi
+
+rm "$tmpfile_o_raw" "$tmpfile_n_raw" "$tmp_new_issues"
+
+exit $rc

tests/patch/dt_binding_check/info.json

@@ -0,0 +1,3 @@
+{
+  "run": ["dt_binding_check.sh"]
+}