libqos/ahci: Add ahci_port_clear helper

Add a helper that assists in clearing out potentially old error and FIS
information from an AHCI port's data structures. This ensures we always
start with a blank slate for interrupt and FIS receipt information.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 1423158090-25580-3-git-send-email-jsnow@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
diff --git a/tests/ahci-test.c b/tests/ahci-test.c
index c689b62..90647f2 100644
--- a/tests/ahci-test.c
+++ b/tests/ahci-test.c
@@ -687,13 +687,8 @@
     i = ahci_port_select(ahci);
     g_test_message("Selected port %u for test", i);
 
-    /* Clear out this port's interrupts (ignore the init register d2h fis) */
-    reg = ahci_px_rreg(ahci, i, AHCI_PX_IS);
-    ahci_px_wreg(ahci, i, AHCI_PX_IS, reg);
-    g_assert_cmphex(ahci_px_rreg(ahci, i, AHCI_PX_IS), ==, 0);
-
-    /* Wipe the FIS-Receive Buffer */
-    qmemset(ahci->port[i].fb, 0x00, 0x100);
+    /* Clear out the FIS Receive area and any pending interrupts. */
+    ahci_port_clear(ahci, i);
 
     /* Create a Command Table buffer. 0x80 is the smallest with a PRDTL of 0. */
     /* We need at least one PRD, so round up to the nearest 0x80 multiple.    */