arm: Implement the 'fake' go command

Implement this feature on ARM for tracing.

It would be nice to have generic bootm support so that it is easily
implemented on any arch.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Albert ARIBAUD <albert.u.boot@aribaud.net>
diff --git a/arch/arm/lib/bootm.c b/arch/arm/lib/bootm.c
index 1b6e0ac..b22fbc9 100644
--- a/arch/arm/lib/bootm.c
+++ b/arch/arm/lib/bootm.c
@@ -68,12 +68,19 @@
 		    gd->bd->bi_dram[0].start + gd->bd->bi_dram[0].size - sp);
 }
 
-static void announce_and_cleanup(void)
+/**
+ * announce_and_cleanup() - Print message and prepare for kernel boot
+ *
+ * @fake: non-zero to do everything except actually boot
+ */
+static void announce_and_cleanup(int fake)
 {
-	printf("\nStarting kernel ...\n\n");
+	printf("\nStarting kernel ...%s\n\n", fake ?
+		"(fake run for tracing)" : "");
 	bootstage_mark_name(BOOTSTAGE_ID_BOOTM_HANDOFF, "start_kernel");
 #ifdef CONFIG_BOOTSTAGE_FDT
-	bootstage_fdt_add_report();
+	if (flag == BOOTM_STATE_OS_FAKE_GO)
+		bootstage_fdt_add_report();
 #endif
 #ifdef CONFIG_BOOTSTAGE_REPORT
 	bootstage_report();
@@ -225,12 +232,13 @@
 }
 
 /* Subcommand: GO */
-static void boot_jump_linux(bootm_headers_t *images)
+static void boot_jump_linux(bootm_headers_t *images, int flag)
 {
 	unsigned long machid = gd->bd->bi_arch_number;
 	char *s;
 	void (*kernel_entry)(int zero, int arch, uint params);
 	unsigned long r2;
+	int fake = (flag & BOOTM_STATE_OS_FAKE_GO);
 
 	kernel_entry = (void (*)(int, int, uint))images->ep;
 
@@ -243,14 +251,15 @@
 	debug("## Transferring control to Linux (at address %08lx)" \
 		"...\n", (ulong) kernel_entry);
 	bootstage_mark(BOOTSTAGE_ID_RUN_OS);
-	announce_and_cleanup();
+	announce_and_cleanup(fake);
 
 	if (IMAGE_ENABLE_OF_LIBFDT && images->ft_len)
 		r2 = (unsigned long)images->ft_addr;
 	else
 		r2 = gd->bd->bi_boot_params;
 
-	kernel_entry(0, machid, r2);
+	if (!fake)
+		kernel_entry(0, machid, r2);
 }
 
 /* Main Entry point for arm bootm implementation
@@ -270,13 +279,13 @@
 		return 0;
 	}
 
-	if (flag & BOOTM_STATE_OS_GO) {
-		boot_jump_linux(images);
+	if (flag & (BOOTM_STATE_OS_GO | BOOTM_STATE_OS_FAKE_GO)) {
+		boot_jump_linux(images, flag);
 		return 0;
 	}
 
 	boot_prep_linux(images);
-	boot_jump_linux(images);
+	boot_jump_linux(images, flag);
 	return 0;
 }