[U-Boot] [PATCH v3] at91: Don't initialize watchdog if CONFIG_SKIP_WATCHDOG_INIT is undefined

[Alexander Stein]

On AT91 the watchdog mode register can only be written once after reset.
If this register is written by u-boot e.g. a Linux driver can't
reconfigure the watchdog later. If the watchdog is left untouched this
is possible. Without touching the mode register the watchdog has a default
setup and u-boot is still able to trigger the watchdog.

Signed-off-by: Alexander Stein <alexander.stein at systec-electronic.com>
---
Changes in v2:
* Add a new specific option CONFIG_SKIP_WATCHDOG_INIT
* Add some documentation

Changes in v3:
* Be more verbose in describing the problem in the commit message and README

 README                                      |   11 +++++++++++
 arch/arm/cpu/arm926ejs/at91/lowlevel_init.S |    2 ++
 2 files changed, 13 insertions(+), 0 deletions(-)

diff --git a/README b/README
index a9c98f2..110668d 100644
--- a/README
+++ b/README
@@ -2817,6 +2817,17 @@ Low Level (hardware related) configuration options:
 		some other boot loader or by a debugger which
 		performs these initializations itself.
 
+- CONFIG_SKIP_WATCHDOG_INIT
+
+		[arm AT91 only] If this variable is defined, then the
+		watchdog will not be programmed upon u-boot start.
+		On AT91 the watchdog mode register can only be written
+		once after reset. If this register is written by u-boot
+		e.g. a Linux driver can't reconfigure the watchdog later. If
+		the watchdog is left untouched this is possible.
+		Without touching the mode register the watchdog has a default
+		setup and u-boot is still able to trigger the watchdog.
+
 - CONFIG_PRELOADER
 
 		Modifies the behaviour of start.S when compiling a loader
diff --git a/arch/arm/cpu/arm926ejs/at91/lowlevel_init.S b/arch/arm/cpu/arm926ejs/at91/lowlevel_init.S
index 559c35c..0645ba8 100644
--- a/arch/arm/cpu/arm926ejs/at91/lowlevel_init.S
+++ b/arch/arm/cpu/arm926ejs/at91/lowlevel_init.S
@@ -186,8 +186,10 @@ SDRAM_setup_end:
 	.ltorg
 
 SMRDATA:
+#ifndef CONFIG_SKIP_WATCHDOG_INIT
 	.word AT91_ASM_WDT_MR
 	.word CONFIG_SYS_WDTC_WDMR_VAL
+#endif
 	/* configure PIOx as EBI0 D[16-31] */
 #if defined(CONFIG_AT91SAM9263)
 	.word AT91_ASM_PIOD_PDR
-- 
1.7.1