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.st...@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
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