ahci: prohibit "restarting" the FIS or CLB engines

If the FIS or DMA engines are already started, do not allow them to be
"restarted." As a side-effect of this change, the migration post-load
routine must be modified to cope. If the engines are listed as "on"
in the migrated registers, they must be cleared to allow the startup
routine to see the transition from "off" to "on".

As a second side-effect, the extra argument to ahci_cond_engine_start
is removed in favor of consistent behavior.

Signed-off-by: John Snow <jsnow@redhat.com>
Message-id: 1454103689-13042-5-git-send-email-jsnow@redhat.com

hw/ide/ahci.c

@@ -199,38 +199,38 @@ static void map_page(AddressSpace *as, uint8_t **ptr, uint64_t addr,
  * Check the cmd register to see if we should start or stop
  * the DMA or FIS RX engines.
  *
- * @ad: Device to engage.
- * @allow_stop: Allow device to transition from started to stopped?
- *   'no' is useful for migration post_load, which does not expect a transition.
+ * @ad: Device to dis/engage.
  *
  * @return 0 on success, -1 on error.
  */
-static int ahci_cond_start_engines(AHCIDevice *ad, bool allow_stop)
+static int ahci_cond_start_engines(AHCIDevice *ad)
 {
     AHCIPortRegs *pr = &ad->port_regs;
+    bool cmd_start = pr->cmd & PORT_CMD_START;
+    bool cmd_on    = pr->cmd & PORT_CMD_LIST_ON;
+    bool fis_start = pr->cmd & PORT_CMD_FIS_RX;
+    bool fis_on    = pr->cmd & PORT_CMD_FIS_ON;
 
-    if (pr->cmd & PORT_CMD_START) {
+    if (cmd_start && !cmd_on) {
         if (!ahci_map_clb_address(ad)) {
+            pr->cmd &= ~PORT_CMD_START;
             error_report("AHCI: Failed to start DMA engine: "
                          "bad command list buffer address");
             return -1;
         }
-    } else if (pr->cmd & PORT_CMD_LIST_ON) {
-        if (allow_stop) {
-            ahci_unmap_clb_address(ad);
-        }
+    } else if (!cmd_start && cmd_on) {
+        ahci_unmap_clb_address(ad);
     }
 
-    if (pr->cmd & PORT_CMD_FIS_RX) {
+    if (fis_start && !fis_on) {
         if (!ahci_map_fis_address(ad)) {
+            pr->cmd &= ~PORT_CMD_FIS_RX;
             error_report("AHCI: Failed to start FIS receive engine: "
                          "bad FIS receive buffer address");
             return -1;
         }
-    } else if (pr->cmd & PORT_CMD_FIS_ON) {
-        if (allow_stop) {
-            ahci_unmap_fis_address(ad);
-        }
+    } else if (!fis_start && fis_on) {
+        ahci_unmap_fis_address(ad);
     }
 
     return 0;
@@ -272,8 +272,8 @@ static void  ahci_port_write(AHCIState *s, int port, int offset, uint32_t val)
             pr->cmd = (pr->cmd & PORT_CMD_RO_MASK) |
                       (val & ~(PORT_CMD_RO_MASK|PORT_CMD_ICC_MASK));
 
-            /* Check FIS RX and CLB engines, allow transition to false: */
-            ahci_cond_start_engines(&s->dev[port], true);
+            /* Check FIS RX and CLB engines */
+            ahci_cond_start_engines(&s->dev[port]);
 
             /* XXX usually the FIS would be pending on the bus here and
                    issuing deferred until the OS enables FIS receival.
@@ -1578,9 +1578,10 @@ static int ahci_state_post_load(void *opaque, int version_id)
             return -1;
         }
 
-        /* Only remap the CLB address if appropriate, disallowing a state
-         * transition from 'on' to 'off' it should be consistent here. */
-        if (ahci_cond_start_engines(ad, false) != 0) {
+        /* After a migrate, the DMA/FIS engines are "off" and
+         * need to be conditionally restarted */
+        pr->cmd &= ~(PORT_CMD_LIST_ON | PORT_CMD_FIS_ON);
+        if (ahci_cond_start_engines(ad) != 0) {
             return -1;
         }