dtc: dt-check-style: Handle properly DTC-style includes

dt-check-style was not properly handling DTC directives (starting with
'/', e.g. /dts-v1/ or /include/), thus a few DTS files had false
positive like:

  apm/apm-merlin.dts:1: [indent-unit-dts] indent unit must be 1 tab in DTS, got '\t\t'

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Link: https://patch.msgid.link/20260709-dts-style-checker-v5-5-fcc147cb697d@oss.qualcomm.com
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>

scripts/dtc/dt-check-style

@@ -49,6 +49,9 @@ re_cpp_directive = re.compile(
     r'^#\s*(include|define|undef|ifdef|ifndef|if|else|elif|endif|'
     r'pragma|error|warning)\b')
 
+re_dtc_directive = re.compile(
+    r'^/(dts-v1|include)/')
+
 # label: name@addr {  -- label and addr optional; name can be "/"
 # Per the DT spec a node name may start with a digit (e.g. 1wire@...).
 # The address part is captured loosely (any non-space, non-brace run) so
@@ -66,7 +69,11 @@ re_ref_node = re.compile(
 
 def is_preprocessor(stripped):
     """Tell C preprocessor directives apart from DTS '#'-prefixed props."""
-    return re_cpp_directive.match(stripped) is not None
+    if re_cpp_directive.match(stripped) is not None:
+        return True
+    if re_dtc_directive.match(stripped) is not None:
+        return True
+    return False
 
 
 class DtsLine:
@@ -178,7 +185,7 @@ def classify_lines(text):
             out.append(dl)
             continue
 
-        if stripped.startswith('#') and is_preprocessor(stripped):
+        if (stripped.startswith('#') or stripped.startswith('/')) and is_preprocessor(stripped):
             dl = DtsLine(i, raw, LineType.PREPROCESSOR,
                          indent_str, stripped)
             dl.depth = depth

scripts/dtc/dt-style-selftest/good/dts-dtc.dts

@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+/*
+ * Test fixture: dtc directive
+ */
+
+/dts-v1/;
+
+/include/ "soc.dtsi"
+/include/"soc-other.dtsi"
+
+/ {
+	compatible = "example,test-board";
+	#address-cells = <1>;
+	#size-cells = <1>;
+
+	leds {
+		led-0 {
+			compatible = "example,led";
+		};
+	};
+};

scripts/dtc/dt-style-selftest/good/dts-preprocessor.dts

@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+/*
+ * Test fixture: preprocessor directive
+ */
+
+/dts-v1/;
+
+#include "soc.dtsi"
+#include<dt-bindings/gpio/gpio.h>
+
+/ {
+	compatible = "example,test-board";
+	#address-cells = <1>;
+	#size-cells = <1>;
+
+	leds {
+		led-0 {
+			compatible = "example,led";
+		};
+	};
+};

scripts/dtc/dt-style-selftest/good/soc.dtsi

@@ -0,0 +1,47 @@
+// SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+/ {
+	#address-cells = <1>;
+	#size-cells = <1>;
+
+	cpus {
+		#address-cells = <1>;
+		#size-cells = <0>;
+
+		cpu@0 {
+			device_type = "cpu";
+			compatible = "arm,cortex-a57";
+			reg = <0x0 0x0>;
+			enable-method = "psci";
+		};
+	};
+
+	pmu {
+		compatible = "example,pmu";
+	};
+
+	soc@0 {
+		compatible = "simple-bus";
+		ranges = <0 0 0 0xc0000000>;
+
+		#address-cells = <1>;
+		#size-cells = <1>;
+
+		interrupt-controller@10000 {
+			compatible = "example,intc";
+			reg = <0x10000 0x1000>;
+			interrupts = <1 2 3>,
+				     <4 5 6>,
+				     <7 8 9>;
+		};
+
+		serial@20000 {
+			compatible = "example,serial";
+			reg = <0x20000 0x1000>;
+		};
+
+		serial@30000 {
+			compatible = "example,serial";
+			reg = <0x30000 0x1000>;
+		};
+	};
+};