Automate DTB regeneration for SMP configuration

This fixes issue where DTB CPU count was inconsistent with runtime hart
count, causing kernel to detect fewer CPUs than specified with '-c'
parameter.

The build system now ensures DTB matches SMP parameter automatically,
eliminating the need for manual "make SMP=X riscv-harts.dtsi minimal.dtb".

Author: jserv

Makefile

@@ -205,8 +205,16 @@ S := $E $E
 CFLAGS += -D SEMU_BOOT_TARGET_TIME=10
 
 SMP ?= 1
+
+# Track SMP value changes to force DTB regeneration
+.smp_stamp: FORCE
+	@if [ ! -f .smp_stamp ] || [ "$$(cat .smp_stamp 2>/dev/null)" != "$(SMP)" ]; then \
+	    echo "$(SMP)" > .smp_stamp; \
+	    rm -f riscv-harts.dtsi minimal.dtb; \
+	fi
+
 .PHONY: riscv-harts.dtsi
-riscv-harts.dtsi:
+riscv-harts.dtsi: .smp_stamp
 	$(Q)python3 scripts/gen-hart-dts.py $@ $(SMP) $(CLOCK_FREQ)
 
 minimal.dtb: minimal.dts riscv-harts.dtsi
@@ -216,6 +224,9 @@ minimal.dtb: minimal.dts riscv-harts.dtsi
 	    $(subst ^,$S,$(filter -D^SEMU_FEATURE_%, $(subst -D$(S)SEMU_FEATURE,-D^SEMU_FEATURE,$(CFLAGS)))) $< \
 	    | $(DTC) - > $@
 
+.PHONY: FORCE
+FORCE:
+
 # Rules for downloading prebuilt Linux kernel image
 include mk/external.mk
 
@@ -245,6 +256,7 @@ clean:
 distclean: clean
 	$(Q)$(RM) riscv-harts.dtsi
 	$(Q)$(RM) minimal.dtb
+	$(Q)$(RM) .smp_stamp
 	$(Q)$(RM) Image rootfs.cpio
 	$(Q)$(RM) ext4.img
 

scripts/verify-dtb.sh

@@ -0,0 +1,41 @@
+#!/bin/bash
+# Verify that DTB CPU count matches expected count
+
+DTB_FILE="${1}"
+EXPECTED_COUNT="${2}"
+
+if [ -z "$DTB_FILE" ] || [ -z "$EXPECTED_COUNT" ]; then
+    echo "Usage: $0 <dtb_file> <expected_cpu_count>"
+    exit 1
+fi
+
+if [ ! -f "$DTB_FILE" ]; then
+    echo "Error: DTB file '$DTB_FILE' not found"
+    exit 1
+fi
+
+# Count CPUs in DTB using dtc
+DTC=$(which dtc 2>/dev/null)
+if [ -z "$DTC" ]; then
+    echo "Warning: dtc not found, skipping DTB verification"
+    exit 0
+fi
+
+CPU_COUNT=$($DTC -I dtb -O dts "$DTB_FILE" 2>/dev/null | grep -c "cpu@")
+
+if [ "$CPU_COUNT" -ne "$EXPECTED_COUNT" ]; then
+    echo "========================================="
+    echo "DTB Configuration Mismatch Detected!"
+    echo "========================================="
+    echo "DTB file '$DTB_FILE' contains $CPU_COUNT CPU(s)"
+    echo "But you requested $EXPECTED_COUNT CPU(s)"
+    echo ""
+    echo "Solution:"
+    echo "  make SMP=$EXPECTED_COUNT riscv-harts.dtsi minimal.dtb"
+    echo ""
+    echo "This will regenerate the DTB with correct CPU count."
+    echo "========================================="
+    exit 1
+fi
+
+exit 0