Keep the LED blinking after failed hard resets

After a failed hard reset, we keep trying to negotiate power.  Before,
the LED was on steady indicating negotiation failure during these
continued negotiations.  Now it keeps blinking, indicating what's
actually going on.

src/device_policy_manager.c

@@ -113,6 +113,11 @@ void pdb_dpm_get_sink_capability(union pd_msg *cap)
         | PD_POWERROLE_SINK | PD_NUMOBJ(numobj);
 }
 
+void pdb_dpm_pd_start(void)
+{
+    chEvtSignal(pdb_led_thread, PDB_EVT_LED_FAST_BLINK);
+}
+
 void pdb_dpm_output_on(void)
 {
     chEvtSignal(pdb_led_thread, PDB_EVT_LED_MEDIUM_BLINK_OFF);

src/device_policy_manager.h

@@ -36,6 +36,11 @@ bool pdb_dpm_evaluate_capability(const union pd_msg *capabilities, union pd_msg
  */
 void pdb_dpm_get_sink_capability(union pd_msg *cap);
 
+/*
+ * Indicate that power negotiations are starting.
+ */
+void pdb_dpm_pd_start(void);
+
 /*
  * Turn on the power output, with LED indication.
  */

src/main.c

@@ -66,6 +66,7 @@ static const I2CConfig i2c2config = {
  */
 static void setup(void)
 {
+    /* Indicate that we're in setup mode */
     chEvtSignal(pdb_led_thread, PDB_EVT_LED_SLOW_BLINK);
 
     /* Disconnect from USB */
@@ -88,8 +89,6 @@ static void setup(void)
  */
 static void pd_buddy(void)
 {
-    chEvtSignal(pdb_led_thread, PDB_EVT_LED_FAST_BLINK);
-
     /* Start I2C2 to make communication with the PHY possible */
     i2cStart(&I2CD2, &i2c2config);
 

src/policy_engine.c

@@ -62,6 +62,7 @@ mailbox_t pdb_pe_mailbox;
 static enum policy_engine_state pe_sink_startup(void)
 {
     explicit_contract = false;
+    pdb_dpm_pd_start();
 
     /* No need to reset the protocol layer here.  There are two ways into this
      * state: startup and exiting hard reset.  On startup, the protocol layer