Split out functions which handle alternative firmware

At present we have all the logic for this feature in VbTryLegacy(). In
preparation for adding a new menu for alternative firmware, split the
logic into two pieces: preparing to start alternative firware, and
cleaning up afterwards if nothing booted.

Also export these functions so that they can be used by the detachable
UI.

BUG=chromium:837018
BRANCH=none
TEST=FEATURES=test emerge-grunt --nodeps vboot_reference

Change-Id: I560634ebb03a7f02a488defa32b83e51001d018e
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1286219
Reviewed-by: Randall Spangler <rspangler@chromium.org>

2 files changed, 58 insertions, 17 deletions

diff --git a/firmware/lib/include/vboot_kernel.h b/firmware/lib/include/vboot_kernel.h
index c3c4585b..15c27101 100644
--- a/firmware/lib/include/vboot_kernel.h
+++ b/firmware/lib/include/vboot_kernel.h
@@ -88,4 +88,38 @@ uint32_t vb2_get_fwmp_flags(void);
  */
 void vb2_nv_commit(struct vb2_context *ctx);
 
+/**
+ * Prepare to start a bootloader
+ *
+ * Get ready to jump into a bootloader if allowed, calling RollbackKernelLock().
+ *
+ * @param allowed 1 if allowed, 0 if not allowed (in which case this function
+ *	prints a debug error)
+ * @return 0 if allowed, -1 if not allowed
+ *
+ */
+int vb2_prepare_alt_fw(int allowed);
+
+/**
+ * Tidy up after failing to start a bootloader
+ *
+ * This beeps twice to indicate failure
+ */
+void vb2_exit_altfw(void);
+
+/**
+ * Jump to a bootloader if possible
+ *
+ * This calls vb2_prepare_alt_fw() to check the operation is permitted. If it
+ * is, then it jumps to the selected bootloader and execution continues there,
+ * never returning.
+ *
+ * If the operation is not permitted, or it is permitted but the bootloader
+ * cannot be found, it calls vb2_exit_altfw() and returns.
+ *
+ * @allowed	1 if allowed, 0 if not allowed
+ * @altfw_num	Number of bootloader to start (0=any, 1=first, etc.)
+ */
+void vb2_try_alt_fw(int allowed, int altfw_num);
+
 #endif  /* VBOOT_REFERENCE_VBOOT_KERNEL_H_ */
diff --git a/firmware/lib/vboot_ui.c b/firmware/lib/vboot_ui.c
index 289e0009..0c4c03dc 100644
--- a/firmware/lib/vboot_ui.c
+++ b/firmware/lib/vboot_ui.c
@@ -72,29 +72,36 @@ static int VbWantShutdown(struct vb2_context *ctx, uint32_t key)
 	return !!shutdown_request;
 }
 
-/**
- * Call out to firmware to boot a numbered boot loader
- *
- * Provided that it is permitted, this function starts up the numbered boot
- * loader.
- *
- * @param altfw_num   Boot loader number to boot (0=any, 1=first, etc.)
- */
-static void VbTryLegacy(int allowed, int altfw_num)
+int vb2_prepare_alt_fw(int allowed)
 {
-	if (!allowed)
+	if (!allowed) {
 		VB2_DEBUG("VbBootDeveloper() - Legacy boot is disabled\n");
-	else if (0 != RollbackKernelLock(0))
+		VbExDisplayDebugInfo("WARNING: Booting legacy BIOS has not "
+				     "been enabled. Refer to the developer"
+				     "-mode documentation for details.\n");
+		return -1;
+	} else if (0 != RollbackKernelLock(0)) {
 		VB2_DEBUG("Error locking kernel versions on legacy boot.\n");
-	else
-		VbExLegacy(altfw_num);	/* will not return if successful */
+		return -1;
+	}
 
-	/* If legacy boot fails, beep and return to calling UI loop. */
+	return 0;
+}
+
+void vb2_exit_altfw(void)
+{
 	VbExBeep(120, 400);
 	VbExSleepMs(120);
 	VbExBeep(120, 400);
 }
 
+void vb2_try_alt_fw(int allowed, int altfw_num)
+{
+	if (!vb2_prepare_alt_fw(allowed))
+		VbExLegacy(altfw_num);	/* will not return if found */
+	vb2_exit_altfw();
+}
+
 uint32_t VbTryUsb(struct vb2_context *ctx)
 {
 	uint32_t retval = VbTryLoadKernel(ctx, VB_DISK_FLAG_REMOVABLE);
@@ -348,7 +355,7 @@ VbError_t vb2_developer_ui(struct vb2_context *ctx)
 		case 0x0c:
 			VB2_DEBUG("VbBootDeveloper() - "
 				  "user pressed Ctrl+L; Try legacy boot\n");
-			VbTryLegacy(allow_legacy, 0);
+			vb2_try_alt_fw(allow_legacy, 0);
 			break;
 
 		case VB_KEY_CTRL_ENTER:
@@ -390,7 +397,7 @@ VbError_t vb2_developer_ui(struct vb2_context *ctx)
 			VB2_DEBUG("VbBootDeveloper() - "
 				  "user pressed key '%c': Boot alternative "
 				  "firmware\n", key);
-			VbTryLegacy(allow_legacy, key - '0');
+			vb2_try_alt_fw(allow_legacy, key - '0');
 			break;
 		default:
 			VB2_DEBUG("VbBootDeveloper() - pressed key %d\n", key);
@@ -406,7 +413,7 @@ VbError_t vb2_developer_ui(struct vb2_context *ctx)
 	/* If defaulting to legacy boot, try that unless Ctrl+D was pressed */
 	if (use_legacy && !ctrl_d_pressed) {
 		VB2_DEBUG("VbBootDeveloper() - defaulting to legacy\n");
-		VbTryLegacy(allow_legacy, 0);
+		vb2_try_alt_fw(allow_legacy, 0);
 	}
 
 	if ((use_usb && !ctrl_d_pressed) && allow_usb) {