Request new power without sending Get_Source_Cap

It was never really necessary to update the source capabilities before
making sending a Request message.  It was convenient though, since we
didn't store the previous Source_Capabilities message.  Now we do, so
it's possible to make a new Request based on that.

This commit makes the Sink do just that.  It doesn't follow the spec's
state diagram for this, but it's a minor change that works better with
this firmware's design, so I don't mind.  There's a comment explaining
that too, so future folks won't be confused by it either.

src/device_policy_manager.c

             chPoolFree(&pdb_msg_pool, (union pd_msg *) pdb_dpm_capabilities);
         }
         pdb_dpm_capabilities = capabilities;
+    } else {
+        /* No new capabilities; use a shorter name for the stored ones. */
+        capabilities = pdb_dpm_capabilities;
     }
 
     /* Get the current configuration */

src/device_policy_manager.h

 
 
 /*
- * Create a Request message based on the given Source_Capabilities message.
+ * Create a Request message based on the given Source_Capabilities message.  If
+ * capabilities is NULL, the last non-null Source_Capabilities message passes
+ * is used.  If none has been provided, the behavior is undefined.
  *
  * Returns true if sufficient power is available, false otherwise.
  */

src/policy_engine.c

     /* Wait for an event */
     if (min_power) {
         evt = chEvtWaitAnyTimeout(PDB_EVT_PE_MSG_RX | PDB_EVT_PE_RESET
-                | PDB_EVT_PE_I_OVRTEMP | PDB_EVT_PE_GET_SOURCE_CAP,
-                PD_T_SINK_REQUEST);
+                | PDB_EVT_PE_I_OVRTEMP | PDB_EVT_PE_GET_SOURCE_CAP
+                | PDB_EVT_PE_NEW_POWER, PD_T_SINK_REQUEST);
     } else {
         evt = chEvtWaitAny(PDB_EVT_PE_MSG_RX | PDB_EVT_PE_RESET
-                | PDB_EVT_PE_I_OVRTEMP | PDB_EVT_PE_GET_SOURCE_CAP);
+                | PDB_EVT_PE_I_OVRTEMP | PDB_EVT_PE_GET_SOURCE_CAP
+                | PDB_EVT_PE_NEW_POWER);
     }
 
     /* If we got reset signaling, transition to default */
         return PESinkGetSourceCap;
     }
 
+    /* If the DPM wants new power, let it figure out what power it wants
+     * exactly.  This isn't exactly the transition from the spec (that would be
+     * SelectCap, not EvalCap), but this works better with the particular
+     * design of this firmware. */
+    if (evt & PDB_EVT_PE_NEW_POWER) {
+        /* Make sure we're evaluating NULL capabilities to use the old ones */
+        if (policy_engine_message != NULL) {
+            chPoolFree(&pdb_msg_pool, policy_engine_message);
+            policy_engine_message = NULL;
+        }
+        return PESinkEvalCap;
+    }
+
     /* If no event was received, the timer ran out. */
     if (evt == 0) {
         /* Repeat our Request message */

src/policy_engine.h

 #define PDB_EVT_PE_HARD_SENT EVENT_MASK(4)
 #define PDB_EVT_PE_I_OVRTEMP EVENT_MASK(5)
 #define PDB_EVT_PE_GET_SOURCE_CAP EVENT_MASK(6)
+#define PDB_EVT_PE_NEW_POWER EVENT_MASK(7)
 
 /* The Policy Engine thread object */
 extern thread_t *pdb_pe_thread;

src/shell.c

 
     pdb_config_flash_update(&tmpcfg);
 
-    chEvtSignal(pdb_pe_thread, PDB_EVT_PE_GET_SOURCE_CAP);
+    chEvtSignal(pdb_pe_thread, PDB_EVT_PE_NEW_POWER);
 }
 
 static void cmd_load(BaseSequentialStream *chp, int argc, char *argv[])