wdt: Wait for timer expiration period before un-gating ARM clock

Allowing the ARM core to resume execution before the reset has
actually fired can lead to undesirable situations such as old
in-memory firmware corrupting a new firmware image just written by a
'write firmware' command.  Add a usleep() call to wdt_perform_reset()
so that it waits the necessary amount of time itself rather than
returning a duration for the caller to wait.

Because the debug UART interface seems to lock up if left active
across a reset, we also bracket the sleep (during which the reset is
expected to occur) with a release/reinit of the bridge interface.

Signed-off-by: Zev Weiss <[email protected]>

src/cmd/reset.c

@@ -20,7 +20,6 @@ int cmd_reset(const char *name __unused, int argc, char *argv[])
 {
     struct host _host, *host = &_host;
     struct soc _soc, *soc = &_soc;
-    int64_t wait = 0;
     struct ahb *ahb;
     struct clk *clk;
     struct wdt *wdt;
@@ -83,11 +82,8 @@ int cmd_reset(const char *name __unused, int argc, char *argv[])
 
     /* wdt_perform_reset ungates the ARM if required */
     logi("Performing SoC reset\n");
-    if ((wait = wdt_perform_reset(wdt)) > 0)
-        usleep(wait);
-
-    /* Cleanup */
-    if (wait < 0) {
+    rc = wdt_perform_reset(wdt);
+    if (rc < 0) {
 clk_enable_arm:
         if ((cleanup = clk_enable(clk, clk_arm)) < 0) {
             errno = -cleanup;

src/cmd/write.c

@@ -163,22 +163,16 @@ int cmd_write(const char *name __unused, int argc, char *argv[])
     if (rc == 0) {
         if (!ahb->drv->local) {
             struct wdt *wdt;
-            int64_t wait;
 
             logi("Performing SoC reset\n");
             if (!(wdt = wdt_get_by_name(soc, "wdt2"))) {
                 loge("Failed to acquire wdt2 controller, exiting\n");
                 goto cleanup_soc;
             }
 
-            wait = wdt_perform_reset(wdt);
-
-            if (wait < 0) {
-                rc = wait;
+            rc = wdt_perform_reset(wdt);
+            if (rc < 0)
                 goto cleanup_soc;
-            }
-
-            usleep(wait);
         }
     } else {
         logi("Deconfiguring VUART host Tx discard\n");

src/soc/wdt.c

@@ -9,6 +9,7 @@
 #include <inttypes.h>
 #include <stdint.h>
 #include <stdio.h>
+#include <unistd.h>
 
 /* Registers */
 #define WDT_RELOAD	        0x04
@@ -119,7 +120,7 @@ static int64_t wdt_usecs_to_ticks(struct wdt *ctx, uint32_t usecs)
     return usecs;
 }
 
-int64_t wdt_perform_reset(struct wdt *ctx)
+int wdt_perform_reset(struct wdt *ctx)
 {
     uint32_t mode;
     int64_t wait;
@@ -159,6 +160,22 @@ int64_t wdt_perform_reset(struct wdt *ctx)
     if ((rc = wdt_writel(ctx, WDT_CTRL, mode)) < 0)
         return rc;
 
+    if ((rc = ahb_release_bridge(ctx->soc->ahb)) < 0)
+        return rc;
+
+    /*
+     * Allow a little extra time for reset to occur (we're timing this
+     * asynchronously after all) before we try to reinitialize the bridge
+     */
+    wait += 1000000;
+    logd("Waiting %"PRId64" microseconds for watchdog timer to expire\n", wait);
+    usleep(wait);
+
+    if ((rc = ahb_reinit_bridge(ctx->soc->ahb)) < 0) {
+        loge("Failed to reinitialize bridge after reset: %d\n", rc);
+        return rc;
+    }
+
     /* The ARM clock gate is sticky on reset?! Ensure it's clear  */
     if ((rc = clk_enable(ctx->clk, clk_arm)) < 0)
         return rc;
@@ -167,7 +184,7 @@ int64_t wdt_perform_reset(struct wdt *ctx)
     if (rc < 0)
         return rc;
 
-    return wait;
+    return 0;
 }
 
 static const struct soc_device_id wdt_match[] = {

src/soc/wdt.h

@@ -12,7 +12,7 @@ int wdt_prevent_reset(struct soc *soc);
 struct wdt;
 
 int wdt_init(struct wdt *ctx, struct soc *soc, const char *name);
-int64_t wdt_perform_reset(struct wdt *ctx);
+int wdt_perform_reset(struct wdt *ctx);
 void wdt_destroy(struct wdt *ctx);
 
 struct wdt *wdt_get_by_name(struct soc *soc, const char *name);