WIP (temporary): krane bring-up init checkpoints painting scanout bands

Diagnostic only, to be reverted before upstreaming: board_early_init_f
(orange), dram_init_banksize (blue), board_early_init_r (red) paint
bands into the depthcharge scanout to localize the early crash.

board/mediatek/mt8183/mt8183.c

@@ -4,6 +4,64 @@
  * Author: Fabien Parent <fparent@baylibre.com>
  */
 
+/*
+ * TEMPORARY bring-up diagnostics (krane Round 13) — do not upstream.
+ * Paint colored bands into the live depthcharge scanout as early-init
+ * checkpoints: full green = wrapper (before U-Boot), orange top band =
+ * board_early_init_f, blue bottom band = dram_init_banksize, red top
+ * band = board_early_init_r. The last one reached localizes the crash;
+ * a successful video probe clears the screen for the banner.
+ */
+#include <cpu_func.h>
+#include <fdtdec.h>
+#include <asm/io.h>
+#include <asm/system.h>
+
+#define DIAG_OVL_L0_ADDR	0x14008f40
+#define DIAG_FB_WIDTH		1200
+#define DIAG_FB_BPL		4800
+#define DIAG_FB_SIZE		0x8ca000
+
+static void diag_paint(u32 y0, u32 rows, u32 color)
+{
+	u32 base = readl((void __iomem *)DIAG_OVL_L0_ADDR);
+	u32 *p, n = rows * DIAG_FB_WIDTH, i;
+
+	if (base < 0x40000000)
+		return;
+
+	if (dcache_status())
+		mmu_map_region(base, DIAG_FB_SIZE, false);
+
+	p = (u32 *)(uintptr_t)(base + (u64)y0 * DIAG_FB_BPL);
+	for (i = 0; i < n; i++)
+		p[i] = color;
+
+	if (dcache_status())
+		flush_dcache_range((uintptr_t)p,
+				   (uintptr_t)(p + n));
+}
+
+int board_early_init_f(void)
+{
+	diag_paint(0, 100, 0x00ff8000);	/* orange */
+	return 0;
+}
+
+void dram_init_banksize(void)
+{
+	fdtdec_setup_memory_banksize();
+	diag_paint(1820, 100, 0x000000ff);	/* blue */
+}
+
+int board_early_init_r(void)
+{
+	diag_paint(0, 100, 0x00ff0000);	/* red */
+	return 0;
+}
+
+/* end TEMPORARY diagnostics */
+
 #include <dm.h>
 #include <net.h>
 

configs/mt8183_kukui_krane_defconfig

@@ -35,6 +35,8 @@ CONFIG_HUSH_PARSER=y
 # CONFIG_CMD_GO is not set
 # CONFIG_CMD_IMI is not set
 CONFIG_BOOTDELAY=-1
+CONFIG_BOARD_EARLY_INIT_F=y
+CONFIG_BOARD_EARLY_INIT_R=y
 # CONFIG_CMD_XIMG is not set
 # CONFIG_CMD_EXPORTENV is not set
 # CONFIG_CMD_IMPORTENV is not set