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>

arch/arm/lib/bootm.c

@@ -68,11 +68,18 @@ void arch_lmb_reserve(struct lmb *lmb)
 		    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
+	if (flag == BOOTM_STATE_OS_FAKE_GO)
 		bootstage_fdt_add_report();
 #endif
 #ifdef CONFIG_BOOTSTAGE_REPORT
@@ -225,12 +232,13 @@ static void boot_prep_linux(bootm_headers_t *images)
 }
 
 /* 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;
 
@@ -243,13 +251,14 @@ static void boot_jump_linux(bootm_headers_t *images)
 	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;
 
+	if (!fake)
 		kernel_entry(0, machid, r2);
 }
 
@@ -270,13 +279,13 @@ int do_bootm_linux(int flag, int argc, char *argv[], bootm_headers_t *images)
 		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;
 }