[U-Boot] [PATCH v2 35/38] x86: Add more comments to the start-up code

[Simon Glass]

The full start-up sequence (TPL->SPL->U-Boot) can be a bit confusing since
each phase has its own 'start' file. Add comments to explain this.

Signed-off-by: Simon Glass <sjg at chromium.org>
---

Changes in v2: None

 arch/x86/cpu/start.S          | 12 ++++++++++++
 arch/x86/cpu/start_from_spl.S |  5 +++--
 arch/x86/cpu/start_from_tpl.S |  3 ++-
 3 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/arch/x86/cpu/start.S b/arch/x86/cpu/start.S
index 9b763942743..01524635e9c 100644
--- a/arch/x86/cpu/start.S
+++ b/arch/x86/cpu/start.S
@@ -2,6 +2,18 @@
 /*
  *  U-Boot - x86 Startup Code
  *
+ * This is always the first code to run from the U-Boot source. To spell it out:
+ *
+ * 1. When TPL (Tertiary Program Loader) is enabled, the boot flow is
+ * TPL->SPL->U-Boot and this file is used for TPL. Then start_from_tpl.S is used
+ * for SPL and start_from_spl.S is used for U-Boot proper.
+ *
+ * 2. When SPL (Secondary Program Loader) is enabled, but not TPL, the boot
+ * flow is SPL->U-Boot and this file is used for SPL. Then start_from_spl.S is
+ * used for U-Boot proper.
+ *
+ * 3. When neither TPL nor SPL is used, this file is used for U-Boot proper.
+ *
  * (C) Copyright 2008-2011
  * Graeme Russ, <graeme.russ at gmail.com>
  *
diff --git a/arch/x86/cpu/start_from_spl.S b/arch/x86/cpu/start_from_spl.S
index 4d4e5d0758d..a73b4d7c459 100644
--- a/arch/x86/cpu/start_from_spl.S
+++ b/arch/x86/cpu/start_from_spl.S
@@ -1,7 +1,8 @@
 /* SPDX-License-Identifier: GPL-2.0+ */
 /*
- * 32-bit x86 Startup Code when running from SPL
- *
+ * 32-bit x86 Startup Code when running from SPL. This is the startup code in
+ * U-Boot proper, when SPL is used.
+
  * Copyright 2018 Google, Inc
  * Written by Simon Glass <sjg at chromium.org>
  */
diff --git a/arch/x86/cpu/start_from_tpl.S b/arch/x86/cpu/start_from_tpl.S
index 44b5363a685..9a4974a5f1b 100644
--- a/arch/x86/cpu/start_from_tpl.S
+++ b/arch/x86/cpu/start_from_tpl.S
@@ -1,6 +1,7 @@
 /* SPDX-License-Identifier: GPL-2.0+ */
 /*
- * 32-bit x86 Startup Code when running from TPL
+ * 32-bit x86 Startup Code when running from TPL. This is the startup code in
+ * SPL, when TPL is used.
  *
  * Copyright 2018 Google, Inc
  * Written by Simon Glass <sjg at chromium.org>
-- 
2.23.0.444.g18eeb5a265-goog