Enable system WDT with timeout of 8s

Enable WDT to ensure the system:

- Does not hang processing any task, such as previous cases of PECI
  commands never completing.
- Does not take longer than the timeout period to complete all
  outstanding tasks.

A timeout of 8s is used to remain close to the existing use of the WDT
in scratch ROM, which was set to 10s.

Signed-off-by: Tim Crawford <tcrawford@system76.com>

src/board/system76/common/include/board/smfi.h

@@ -6,7 +6,6 @@
 #include <stdint.h>
 
 void smfi_init(void);
-void smfi_watchdog(void);
 void smfi_event(void);
 void smfi_debug(uint8_t byte);
 

src/board/system76/common/main.c

@@ -30,6 +30,7 @@
 #include <common/macro.h>
 #include <common/version.h>
 #include <ec/ec.h>
+#include <ec/etwd.h>
 
 #ifdef PARALLEL_DEBUG
 #include <board/parallel.h>
@@ -96,6 +97,8 @@ void main(void) {
     gpio_debug();
 #endif
 
+    wdt_init();
+
     INFO("System76 EC board '%s', version '%s'\n", board(), version());
 
     systick_t last_time_100ms = 0;
@@ -160,6 +163,9 @@ void main(void) {
         pmc_event(&PMC_1);
         // AP/EC communication over SMFI
         smfi_event();
+
+        wdt_kick();
+
         // Idle until next timer interrupt
         //Disabled until interrupts used: PCON |= 1;
     }

src/board/system76/common/scratch.c

@@ -4,6 +4,7 @@
 #include <board/fan.h>
 #include <board/smfi.h>
 #include <common/macro.h>
+#include <ec/etwd.h>
 #include <ec/pwm.h>
 #include <ec/scratch.h>
 
@@ -25,8 +26,8 @@ void scratch_trampoline(void) {
 
     //TODO: Clear keyboard presses
 
-    // Start watchdog timer
-    smfi_watchdog();
+    // Restart WDT before entry to scratch ROM
+    wdt_kick();
 
     // Disable interrupts
     EA = 0;

src/board/system76/common/smfi.c

@@ -337,26 +337,17 @@ static enum Result cmd_reset(void) {
 
 #endif // !defined(__SCRATCH__)
 
-    // Attempt to trigger watchdog reset
-    ETWCFG |= BIT(5);
-    EWDKEYR = 0;
+    wdt_trigger();
 
     // Failed if it got this far
     return RES_ERR;
 }
 
-// Set a watchdog timer of 10 seconds
-void smfi_watchdog(void) {
-    ET1CNTLLR = 0xFF;
-    EWDCNTLLR = 0xFF;
-    EWDCNTLHR = 0x04;
-}
-
 void smfi_event(void) {
     if (smfi_cmd[SMFI_CMD_CMD]) {
 #if defined(__SCRATCH__)
         // If in scratch ROM, restart watchdog timer when command received
-        smfi_watchdog();
+        wdt_kick();
 #endif
 
         switch (smfi_cmd[SMFI_CMD_CMD]) {

src/ec/ite/ec.mk

@@ -2,6 +2,7 @@
 
 ec-y += ec.c
 ec-$(CONFIG_BUS_ESPI) += espi.c
+ec-y += etwd.c
 ec-y += gpio.c
 ec-y += i2c.c
 ec-y += intc.c

src/ec/ite/etwd.c

@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: GPL-3.0-only
+
+// External Timer and External Watchdog (ETWD)
+
+#include <ec/etwd.h>
+#include <common/macro.h>
+
+enum EwtCfg {
+    // Lock EWTCFG register
+    LETWCFG = BIT(0),
+    // Lock ET1PS register
+    LETPS1 = BIT(1),
+    // Lock ET1CNTLx registers
+    LET1CNTL = BIT(2),
+    // Lock EWDCNTLx registers
+    LEWDCNTL = BIT(3),
+    // External WDT clock source
+    EWDSRC = BIT(4),
+    // Enable key match function to touch the WDT
+    EWDKEYEN = BIT(5),
+    // Lock ET1 and EWDT registers
+    LOCK_ALL = LETWCFG | LETPS1 | LET1CNTL | LEWDCNTL,
+};
+
+enum EtwdPrescaler {
+    ETWD_PRESCALER_32768_HZ = 0,
+    ETWD_PRESCALER_1024_HZ = 1,
+    ETWD_PRESCALER_32_HZ = 2,
+    ETWD_PRESCALER_EC_CLK = 3,      // Not available for ET1PS
+};
+
+void wdt_init(void) {
+    ET1PSR = ETWD_PRESCALER_1024_HZ;
+    ETWCFG = EWDKEYEN | EWDSRC;
+
+    // Start ET1 so EWDT can be started
+    ET1CNTLLR = 0xFF;
+
+    // Start EWDT with timeout of 8s
+    // TODO: Determine time based on system performance or requirement
+    EWDCNTLHR = 0x20;
+    EWDCNTLLR = 0;
+
+    ETWCFG |= LOCK_ALL;
+}

src/ec/ite/include/ec/etwd.h

@@ -1,7 +1,9 @@
 // SPDX-License-Identifier: GPL-3.0-only
 
-#ifndef _EC_ECWD_H
-#define _EC_ECWD_H
+// External Timer and External Watchdog (ETWD)
+
+#ifndef _EC_ETWD_H
+#define _EC_ETWD_H
 
 #include <stdint.h>
 
@@ -27,4 +29,22 @@ volatile uint8_t __xdata __at(0x1F13) ET3CNTLH2R;
 volatile uint8_t __xdata __at(0x1F16) ET4CNTLLR;
 #endif
 
-#endif // _EC_ECWD_H
+// When the key match function of EWD is enabled (EWTCFG[5]), writing this
+// value to EWDKEY will restart the WDT.
+#define WDT_KEY 0x5C
+
+void wdt_init(void);
+
+// Restart WDT
+// NOTE: Must be inlined for compiling in Scratch ROM
+static inline void wdt_kick(void) {
+    EWDKEYR = WDT_KEY;
+}
+
+// Trigger EC reset by WDT key mismatch
+// NOTE: Must be inlined for compiling in Scratch ROM
+static inline void wdt_trigger(void) {
+    EWDKEYR = 0;
+}
+
+#endif // _EC_ETWD_H