[U-Boot] [RFC 02/11] spl: Allow skipping clearing BSS during relocation

[Andreas Dannenberg <dannenberg@ti.com>]

On some platform we have sufficient memory available early on to allow
setting up and using a basic BSS prior to relocation. In order to be
able to preserve data written to BSS during early startup add a Kconfig
option allowing to skip the clearing of the BSS section during setting
up of the final environment / relocation.

Signed-off-by: Andreas Dannenberg <dannenberg@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
---
 arch/arm/lib/crt0.S |  3 +++
 common/spl/Kconfig  | 13 +++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/arch/arm/lib/crt0.S b/arch/arm/lib/crt0.S
index 30fba20e1b..e24833a6f8 100644
--- a/arch/arm/lib/crt0.S
+++ b/arch/arm/lib/crt0.S
@@ -126,6 +126,8 @@ here:
 	movne	sp, r0
 	movne	r9, r0
 # endif
+
+#if !CONFIG_IS_ENABLED(SKIP_CLEAR_BSS)
 	ldr	r0, =__bss_start	/* this is auto-relocated! */
 
 #ifdef CONFIG_USE_ARCH_MEMSET
@@ -143,6 +145,7 @@ clbss_l:cmp	r0, r1			/* while not at end of BSS */
 	addlo	r0, r0, #4		/* move to next */
 	blo	clbss_l
 #endif
+#endif
 
 #if ! defined(CONFIG_SPL_BUILD)
 	bl coloured_LED_init
diff --git a/common/spl/Kconfig b/common/spl/Kconfig
index c7cd34449a..098cbb2f7f 100644
--- a/common/spl/Kconfig
+++ b/common/spl/Kconfig
@@ -188,6 +188,19 @@ config TPL_BANNER_PRINT
 	  info. Disabling this option could be useful to reduce SPL boot time
 	  (e.g. approx. 6 ms faster, when output on i.MX6 with 115200 baud).
 
+
+config SPL_SKIP_CLEAR_BSS
+	depends on ARM && !ARM64
+	bool "Skips clearing BSS section during environment setup / relocation"
+	help
+	  On some platform we have sufficient memory available early on to
+	  allow setting up and using a basic BSS prior to relocation. In order
+	  to preserve data written to BSS during early startup use use this
+	  option to skip the clearing of the BSS section. Note that activating
+	  this option implies that you are responsible for clearing the BSS
+	  section yourself, otherwise you will most likely end up with an
+	  invalid post-relocation environment.
+
 config SPL_DISPLAY_PRINT
 	bool "Display a board-specific message in SPL"
 	help
-- 
2.17.1