[S] Change in coreboot[master]: soc/mediatek/common: Reset the watchdog timer before triggering reset.

[KuanHsun Cheng (Code Review)]

Attention is currently required from: Allen-KH Cheng.

Hello Allen-KH Cheng,

I'd like you to do a code review.
Please visit

https://review.coreboot.org/c/coreboot/+/71754

to review the following change.

Change subject: soc/mediatek/common: Reset the watchdog timer before triggering reset.
......................................................................

soc/mediatek/common: Reset the watchdog timer before triggering reset.

When the watchdog timer reaches 0, the timer value won't reset to the
default value unless there is an external reset or a kick. It will
result in the watchdog failing to trigger the reset signal.

We kick the watchdog to reset the timer to the default value. Also, add
a 100 us delay before triggering the reset signal.

BUG=b:264003005, b:264017048
BRANCH=corsola
TEST= Reboot successfully with the following cmd
stop daisydog
sleep 60 > /dev/watchdog&

Signed-off-by: Runyang Chen 
Signed-off-by: Allen-kh Cheng 
Change-Id: Ic4964103d54910c4a1e675b59c362e93c2213b19
---
M src/soc/mediatek/common/include/soc/wdt_common.h
M src/soc/mediatek/common/wdt.c
2 files changed, 32 insertions(+), 0 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/54/71754/1

diff --git a/src/soc/mediatek/common/include/soc/wdt_common.h b/src/soc/mediatek/common/include/soc/wdt_common.h
index 5587d50..6d6d2ba 100644
--- a/src/soc/mediatek/common/include/soc/wdt_common.h
+++ b/src/soc/mediatek/common/include/soc/wdt_common.h
@@ -32,6 +32,11 @@
    MTK_WDT_MODE_ENABLE	= 1 << 0
 };

+/* WDT_RESTART */
+enum {
+	MTK_WDT_RESTART_KEY	= 0x1971
+};
+
 /* WDT_RESET */
 enum {
    MTK_WDT_SWRST_KEY	= 0x1209,
diff --git a/src/soc/mediatek/common/wdt.c b/src/soc/mediatek/common/wdt.c
index 7ae4661..663fc2f 100644
--- a/src/soc/mediatek/common/wdt.c
+++ b/src/soc/mediatek/common/wdt.c
@@ -1,6 +1,7 @@
 /* SPDX-License-Identifier: GPL-2.0-only */

#include <arch/cache.h>
+#include <delay.h>
 #include <device/mmio.h>
 #include <console/console.h>
 #include <halt.h>
@@ -23,7 +24,9 @@
    printk(BIOS_INFO, "%s() called!\n", __func__);

dcache_clean_all();
+	write32(&mtk_wdt->wdt_restart, MTK_WDT_RESTART_KEY);
    setbits32(&mtk_wdt->wdt_mode, MTK_WDT_MODE_EXTEN | MTK_WDT_MODE_KEY);
+	udelay(100);
    write32(&mtk_wdt->wdt_swrst, MTK_WDT_SWRST_KEY);

halt();