Index: sys/dev/ahci/ahci.c
===================================================================
--- sys/dev/ahci/ahci.c	(revision 220643)
+++ sys/dev/ahci/ahci.c	(working copy)
@@ -250,7 +250,7 @@ static struct {
 	{0x0abe10de, 0x00, "NVIDIA MCP79",	AHCI_Q_NOAA},
 	{0x0abf10de, 0x00, "NVIDIA MCP79",	AHCI_Q_NOAA},
 	{0x0d8410de, 0x00, "NVIDIA MCP89",	AHCI_Q_NOAA},
-	{0x0d8510de, 0x00, "NVIDIA MCP89",	AHCI_Q_NOAA},
+	{0x0d8510de, 0x00, "NVIDIA MCP89",	AHCI_Q_NOFORCE|AHCI_Q_NOAA},
 	{0x0d8610de, 0x00, "NVIDIA MCP89",	AHCI_Q_NOAA},
 	{0x0d8710de, 0x00, "NVIDIA MCP89",	AHCI_Q_NOAA},
 	{0x0d8810de, 0x00, "NVIDIA MCP89",	AHCI_Q_NOAA},
Index: sys/dev/ata/chipsets/ata-nvidia.c
===================================================================
--- sys/dev/ata/chipsets/ata-nvidia.c	(revision 220643)
+++ sys/dev/ata/chipsets/ata-nvidia.c	(working copy)
@@ -170,6 +170,8 @@ ata_nvidia_probe(device_t dev)
      { ATA_NFORCE_MCP89_AA, 0, NVAHCI,  0, ATA_SA300, "nForce MCP89" },
      { ATA_NFORCE_MCP89_AB, 0, NVAHCI,  0, ATA_SA300, "nForce MCP89" },
      { 0, 0, 0, 0, 0, 0}} ;
+    static struct ata_chip_id quirk_apple_mcp89 =
+	{ ATA_NFORCE_MCP89_A1, 0, 0, 0, ATA_UDMA2, "nForce MCP89" };
 
     if (pci_get_vendor(dev) != ATA_NVIDIA_ID)
 	return ENXIO;
@@ -177,6 +179,14 @@ ata_nvidia_probe(device_t dev)
     if (!(ctlr->chip = ata_match_chip(dev, ids)))
 	return ENXIO;
 
+    /*
+     * XXX Recent Apple Mac with this chipset does not initialize AHCI mode
+     * unless it is started from EFI loader.  However, ATA compat mode works.
+     */
+    if (ctlr->chip->chipid == ATA_NFORCE_MCP89_A1 &&
+	pci_get_subclass(dev) == PCIS_STORAGE_IDE)
+	ctlr->chip = &quirk_apple_mcp89;
+
     ata_set_desc(dev);
     if (ctlr->chip->cfg1 & NVAHCI)
 	ctlr->chipinit = ata_ahci_chipinit;