diff --git a/src/arch/x86/core/pcidirect.c b/src/arch/x86/core/pcidirect.c
index 9b8e6b1d..0d09be84 100644
--- a/src/arch/x86/core/pcidirect.c
+++ b/src/arch/x86/core/pcidirect.c
@@ -36,10 +36,12 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
  * Prepare for Type 1 PCI configuration space access
  *
  * @v pci		PCI device
- * @v where	Location within PCI configuration space
+ * @v where		Location within PCI configuration space
  */
 void pcidirect_prepare ( struct pci_device *pci, int where ) {
-	outl ( ( 0x80000000 | ( pci->busdevfn << 8 ) | ( where & ~3 ) ),
+	uint16_t busdevfn = ( pci->busdevfn & 0xffff );
+
+	outl ( ( 0x80000000 | ( busdevfn << 8 ) | ( where & ~3 ) ),
 	       PCIDIRECT_CONFIG_ADDRESS );
 }
 
diff --git a/src/core/settings.c b/src/core/settings.c
index 75755578..9cae0cae 100644
--- a/src/core/settings.c
+++ b/src/core/settings.c
@@ -2232,6 +2232,10 @@ static int format_busdevfn_setting ( const struct setting_type *type __unused,
 				     const void *raw, size_t raw_len, char *buf,
 				     size_t len ) {
 	unsigned long busdevfn;
+	unsigned int seg;
+	unsigned int bus;
+	unsigned int slot;
+	unsigned int func;
 	int check_len;
 
 	/* Extract numeric value */
@@ -2240,9 +2244,14 @@ static int format_busdevfn_setting ( const struct setting_type *type __unused,
 		return check_len;
 	assert ( check_len == ( int ) raw_len );
 
+	/* Extract PCI address components */
+	seg = PCI_SEG ( busdevfn );
+	bus = PCI_BUS ( busdevfn );
+	slot = PCI_SLOT ( busdevfn );
+	func = PCI_FUNC ( busdevfn );
+
 	/* Format value */
-	return snprintf ( buf, len, "%02lx:%02lx.%lx", PCI_BUS ( busdevfn ),
-			  PCI_SLOT ( busdevfn ), PCI_FUNC ( busdevfn ) );
+	return snprintf ( buf, len, "%04x:%02x:%02x.%x", seg, bus, slot, func );
 }
 
 /** PCI bus:dev.fn setting type */
diff --git a/src/drivers/bus/pci.c b/src/drivers/bus/pci.c
index 6fbedd94..06b36a77 100644
--- a/src/drivers/bus/pci.c
+++ b/src/drivers/bus/pci.c
@@ -175,7 +175,7 @@ void adjust_pci_device ( struct pci_device *pci ) {
  * @ret rc		Return status code
  */
 int pci_read_config ( struct pci_device *pci ) {
-	uint16_t busdevfn;
+	uint32_t busdevfn;
 	uint8_t hdrtype;
 	uint32_t tmp;
 
@@ -203,8 +203,8 @@ int pci_read_config ( struct pci_device *pci ) {
 	pci_read_bases ( pci );
 
 	/* Initialise generic device component */
-	snprintf ( pci->dev.name, sizeof ( pci->dev.name ),
-		   "PCI%02x:%02x.%x", PCI_BUS ( pci->busdevfn ),
+	snprintf ( pci->dev.name, sizeof ( pci->dev.name ), "%04x:%02x:%02x.%x",
+		   PCI_SEG ( pci->busdevfn ), PCI_BUS ( pci->busdevfn ),
 		   PCI_SLOT ( pci->busdevfn ), PCI_FUNC ( pci->busdevfn ) );
 	pci->dev.desc.bus_type = BUS_TYPE_PCI;
 	pci->dev.desc.location = pci->busdevfn;
@@ -232,7 +232,7 @@ int pci_find_next ( struct pci_device *pci, unsigned int busdevfn ) {
 
 	/* Determine number of PCI buses */
 	if ( ! end )
-		end = PCI_BUSDEVFN ( pci_num_bus(), 0, 0 );
+		end = PCI_BUSDEVFN ( 0, pci_num_bus(), 0, 0 );
 
 	/* Find next PCI device, if any */
 	for ( ; busdevfn < end ; busdevfn++ ) {
diff --git a/src/drivers/bus/pci_settings.c b/src/drivers/bus/pci_settings.c
index 1cb9fa5a..98005559 100644
--- a/src/drivers/bus/pci_settings.c
+++ b/src/drivers/bus/pci_settings.c
@@ -70,7 +70,7 @@ static int pci_settings_fetch ( struct settings *settings __unused,
 	unsigned int i;
 
 	/* Extract busdevfn, offset, and length from tag */
-	tag_busdevfn = ( ( setting->tag >> 16 ) & 0xffff );
+	tag_busdevfn = ( setting->tag >> 16 );
 	tag_offset = ( ( setting->tag >> 8 ) & 0xff );
 	tag_len = ( ( setting->tag >> 0 ) & 0xff );
 
diff --git a/src/drivers/net/phantom/phantom.c b/src/drivers/net/phantom/phantom.c
index 38b66743..781049ff 100644
--- a/src/drivers/net/phantom/phantom.c
+++ b/src/drivers/net/phantom/phantom.c
@@ -2060,6 +2060,7 @@ static int phantom_probe ( struct pci_device *pci ) {
 	struct net_device *netdev;
 	struct phantom_nic *phantom;
 	struct settings *parent_settings;
+	unsigned int busdevfn;
 	int rc;
 
 	/* Allocate Phantom device */
@@ -2090,19 +2091,20 @@ static int phantom_probe ( struct pci_device *pci ) {
 	 * B2 will have this fixed; remove this hack when B1 is no
 	 * longer in use.
 	 */
-	if ( PCI_FUNC ( pci->busdevfn ) == 0 ) {
+	busdevfn = pci->busdevfn;
+	if ( PCI_FUNC ( busdevfn ) == 0 ) {
 		unsigned int i;
 		for ( i = 0 ; i < 8 ; i++ ) {
 			uint32_t temp;
 			pci->busdevfn =
-				PCI_BUSDEVFN ( PCI_BUS ( pci->busdevfn ),
-					       PCI_SLOT ( pci->busdevfn ), i );
+				PCI_BUSDEVFN ( PCI_SEG ( busdevfn ),
+					       PCI_BUS ( busdevfn ),
+					       PCI_SLOT ( busdevfn ), i );
 			pci_read_config_dword ( pci, 0xc8, &temp );
 			pci_read_config_dword ( pci, 0xc8, &temp );
 			pci_write_config_dword ( pci, 0xc8, 0xf1000 );
 		}
-		pci->busdevfn = PCI_BUSDEVFN ( PCI_BUS ( pci->busdevfn ),
-					       PCI_SLOT ( pci->busdevfn ), 0 );
+		pci->busdevfn = busdevfn;
 	}
 
 	/* Initialise the command PEG */
diff --git a/src/include/ipxe/pci.h b/src/include/ipxe/pci.h
index bf0e81df..ddd8c8d1 100644
--- a/src/include/ipxe/pci.h
+++ b/src/include/ipxe/pci.h
@@ -195,8 +195,8 @@ struct pci_device {
 	uint32_t class;
 	/** Interrupt number */
 	uint8_t irq;
-	/** Bus, device, and function (bus:dev.fn) number */
-	uint16_t busdevfn;
+	/** Segment, bus, device, and function (bus:dev.fn) number */
+	uint32_t busdevfn;
 	/** Driver for this device */
 	struct pci_driver *driver;
 	/** Driver-private data
@@ -241,11 +241,13 @@ struct pci_driver {
 /** Declare a fallback PCI driver */
 #define __pci_driver_fallback __table_entry ( PCI_DRIVERS, 02 )
 
+#define PCI_SEG( busdevfn )		( ( (busdevfn) >> 16 ) & 0xffff )
 #define PCI_BUS( busdevfn )		( ( (busdevfn) >> 8 ) & 0xff )
 #define PCI_SLOT( busdevfn )		( ( (busdevfn) >> 3 ) & 0x1f )
 #define PCI_FUNC( busdevfn )		( ( (busdevfn) >> 0 ) & 0x07 )
-#define PCI_BUSDEVFN( bus, slot, func )	\
-	( ( (bus) << 8 ) | ( (slot) << 3 ) | ( (func) << 0 ) )
+#define PCI_BUSDEVFN( segment, bus, slot, func )			\
+	( ( (segment) << 16 ) | ( (bus) << 8 ) |			\
+	  ( (slot) << 3 ) | ( (func) << 0 ) )
 #define PCI_FIRST_FUNC( busdevfn )	( (busdevfn) & ~0x07 )
 #define PCI_LAST_FUNC( busdevfn )	( (busdevfn) | 0x07 )
 
@@ -271,12 +273,12 @@ struct pci_driver {
 	PCI_ID( _vendor, _device, _name, _description, _data )
 
 /** PCI device debug message format */
-#define PCI_FMT "PCI %02x:%02x.%x"
+#define PCI_FMT "%04x:%02x:%02x.%x"
 
 /** PCI device debug message arguments */
 #define PCI_ARGS( pci )							\
-	PCI_BUS ( (pci)->busdevfn ), PCI_SLOT ( (pci)->busdevfn ),	\
-	PCI_FUNC ( (pci)->busdevfn )
+	PCI_SEG ( (pci)->busdevfn ), PCI_BUS ( (pci)->busdevfn ),	\
+	PCI_SLOT ( (pci)->busdevfn ), PCI_FUNC ( (pci)->busdevfn )
 
 extern void adjust_pci_device ( struct pci_device *pci );
 extern unsigned long pci_bar_start ( struct pci_device *pci,
diff --git a/src/interface/bofm/bofm.c b/src/interface/bofm/bofm.c
index 545088dc..54039193 100644
--- a/src/interface/bofm/bofm.c
+++ b/src/interface/bofm/bofm.c
@@ -313,12 +313,12 @@ int bofm ( userptr_t bofmtab, struct pci_device *pci ) {
 		}
 		DBG ( "BOFM: slot %d port %d%s is " PCI_FMT " mport %d\n",
 		      en.slot, ( en.port + 1 ),
-		      ( ( en.slot || en.port ) ? "" : "(?)" ),
+		      ( ( en.slot || en.port ) ? "" : "(?)" ), 0,
 		      PCI_BUS ( en.busdevfn ), PCI_SLOT ( en.busdevfn ),
 		      PCI_FUNC ( en.busdevfn ), en.mport );
 		bofm = bofm_find_busdevfn ( en.busdevfn );
 		if ( ! bofm ) {
-			DBG ( "BOFM: " PCI_FMT " mport %d ignored\n",
+			DBG ( "BOFM: " PCI_FMT " mport %d ignored\n", 0,
 			      PCI_BUS ( en.busdevfn ), PCI_SLOT ( en.busdevfn ),
 			      PCI_FUNC ( en.busdevfn ), en.mport );
 			continue;
diff --git a/src/interface/efi/efi_pci.c b/src/interface/efi/efi_pci.c
index be305ba6..9f0851a5 100644
--- a/src/interface/efi/efi_pci.c
+++ b/src/interface/efi/efi_pci.c
@@ -61,58 +61,157 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
  ******************************************************************************
  */
 
-/** PCI root bridge I/O protocol */
-static EFI_PCI_ROOT_BRIDGE_IO_PROTOCOL *efipci;
-EFI_REQUEST_PROTOCOL ( EFI_PCI_ROOT_BRIDGE_IO_PROTOCOL, &efipci );
+/**
+ * Locate EFI PCI root bridge I/O protocol
+ *
+ * @v pci		PCI device
+ * @ret handle		EFI PCI root bridge handle
+ * @ret root		EFI PCI root bridge I/O protocol, or NULL if not found
+ * @ret rc		Return status code
+ */
+static int efipci_root ( struct pci_device *pci, EFI_HANDLE *handle,
+			 EFI_PCI_ROOT_BRIDGE_IO_PROTOCOL **root ) {
+	EFI_BOOT_SERVICES *bs = efi_systab->BootServices;
+	EFI_HANDLE *handles;
+	UINTN num_handles;
+	union {
+		void *interface;
+		EFI_PCI_ROOT_BRIDGE_IO_PROTOCOL *root;
+	} u;
+	EFI_STATUS efirc;
+	UINTN i;
+	int rc;
 
+	/* Enumerate all handles */
+	if ( ( efirc = bs->LocateHandleBuffer ( ByProtocol,
+			&efi_pci_root_bridge_io_protocol_guid,
+			NULL, &num_handles, &handles ) ) != 0 ) {
+		rc = -EEFI ( efirc );
+		DBGC ( pci, "EFIPCI cannot locate root bridges: %s\n",
+		       strerror ( rc ) );
+		goto err_locate;
+	}
+
+	/* Look for matching root bridge I/O protocol */
+	for ( i = 0 ; i < num_handles ; i++ ) {
+		*handle = handles[i];
+		if ( ( efirc = bs->OpenProtocol ( *handle,
+				&efi_pci_root_bridge_io_protocol_guid,
+				&u.interface, efi_image_handle, *handle,
+				EFI_OPEN_PROTOCOL_GET_PROTOCOL ) ) != 0 ) {
+			rc = -EEFI ( efirc );
+			DBGC ( pci, "EFIPCI cannot open %s: %s\n",
+			       efi_handle_name ( *handle ), strerror ( rc ) );
+			continue;
+		}
+		if ( u.root->SegmentNumber == PCI_SEG ( pci->busdevfn ) ) {
+			*root = u.root;
+			bs->FreePool ( handles );
+			return 0;
+		}
+		bs->CloseProtocol ( *handle,
+				    &efi_pci_root_bridge_io_protocol_guid,
+				    efi_image_handle, *handle );
+	}
+	DBGC ( pci, "EFIPCI found no root bridge for " PCI_FMT "\n",
+	       PCI_ARGS ( pci ) );
+	rc = -ENOENT;
+
+	bs->FreePool ( handles );
+ err_locate:
+	return rc;
+}
+
+/**
+ * Calculate EFI PCI configuration space address
+ *
+ * @v pci		PCI device
+ * @v location		Encoded offset and width
+ * @ret address		EFI PCI address
+ */
 static unsigned long efipci_address ( struct pci_device *pci,
 				      unsigned long location ) {
+
 	return EFI_PCI_ADDRESS ( PCI_BUS ( pci->busdevfn ),
 				 PCI_SLOT ( pci->busdevfn ),
 				 PCI_FUNC ( pci->busdevfn ),
 				 EFIPCI_OFFSET ( location ) );
 }
 
+/**
+ * Read from PCI configuration space
+ *
+ * @v pci		PCI device
+ * @v location		Encoded offset and width
+ * @ret value		Value
+ * @ret rc		Return status code
+ */
 int efipci_read ( struct pci_device *pci, unsigned long location,
 		  void *value ) {
+	EFI_BOOT_SERVICES *bs = efi_systab->BootServices;
+	EFI_PCI_ROOT_BRIDGE_IO_PROTOCOL *root;
+	EFI_HANDLE handle;
 	EFI_STATUS efirc;
 	int rc;
 
-	if ( ! efipci )
-		return -ENOTSUP;
+	/* Identify root bridge */
+	if ( ( rc = efipci_root ( pci, &handle, &root ) ) != 0 )
+		goto err_root;
 
-	if ( ( efirc = efipci->Pci.Read ( efipci, EFIPCI_WIDTH ( location ),
-					  efipci_address ( pci, location ), 1,
-					  value ) ) != 0 ) {
+	/* Read from configuration space */
+	if ( ( efirc = root->Pci.Read ( root, EFIPCI_WIDTH ( location ),
+					efipci_address ( pci, location ), 1,
+					value ) ) != 0 ) {
 		rc = -EEFI ( efirc );
 		DBG ( "EFIPCI config read from " PCI_FMT " offset %02lx "
 		      "failed: %s\n", PCI_ARGS ( pci ),
 		      EFIPCI_OFFSET ( location ), strerror ( rc ) );
-		return -EIO;
+		goto err_read;
 	}
 
-	return 0;
+ err_read:
+	bs->CloseProtocol ( handle, &efi_pci_root_bridge_io_protocol_guid,
+			    efi_image_handle, handle );
+ err_root:
+	return rc;
 }
 
+/**
+ * Write to PCI configuration space
+ *
+ * @v pci		PCI device
+ * @v location		Encoded offset and width
+ * @v value		Value
+ * @ret rc		Return status code
+ */
 int efipci_write ( struct pci_device *pci, unsigned long location,
 		   unsigned long value ) {
+	EFI_BOOT_SERVICES *bs = efi_systab->BootServices;
+	EFI_PCI_ROOT_BRIDGE_IO_PROTOCOL *root;
+	EFI_HANDLE handle;
 	EFI_STATUS efirc;
 	int rc;
 
-	if ( ! efipci )
-		return -ENOTSUP;
+	/* Identify root bridge */
+	if ( ( rc = efipci_root ( pci, &handle, &root ) ) != 0 )
+		goto err_root;
 
-	if ( ( efirc = efipci->Pci.Write ( efipci, EFIPCI_WIDTH ( location ),
-					   efipci_address ( pci, location ), 1,
-					   &value ) ) != 0 ) {
+	/* Read from configuration space */
+	if ( ( efirc = root->Pci.Write ( root, EFIPCI_WIDTH ( location ),
+					 efipci_address ( pci, location ), 1,
+					 &value ) ) != 0 ) {
 		rc = -EEFI ( efirc );
 		DBG ( "EFIPCI config write to " PCI_FMT " offset %02lx "
 		      "failed: %s\n", PCI_ARGS ( pci ),
 		      EFIPCI_OFFSET ( location ), strerror ( rc ) );
-		return -EIO;
+		goto err_write;
 	}
 
-	return 0;
+ err_write:
+	bs->CloseProtocol ( handle, &efi_pci_root_bridge_io_protocol_guid,
+			    efi_image_handle, handle );
+ err_root:
+	return rc;
 }
 
 PROVIDE_PCIAPI_INLINE ( efi, pci_num_bus );
@@ -146,6 +245,7 @@ int efipci_open ( EFI_HANDLE device, UINT32 attributes,
 		void *interface;
 	} pci_io;
 	UINTN pci_segment, pci_bus, pci_dev, pci_fn;
+	unsigned int busdevfn;
 	EFI_STATUS efirc;
 	int rc;
 
@@ -190,7 +290,8 @@ int efipci_open ( EFI_HANDLE device, UINT32 attributes,
 				    EFI_PCI_IO_ATTRIBUTE_BUS_MASTER, NULL );
 
 	/* Populate PCI device */
-	pci_init ( pci, PCI_BUSDEVFN ( pci_bus, pci_dev, pci_fn ) );
+	busdevfn = PCI_BUSDEVFN ( pci_segment, pci_bus, pci_dev, pci_fn );
+	pci_init ( pci, busdevfn );
 	if ( ( rc = pci_read_config ( pci ) ) != 0 ) {
 		DBGC ( device, "EFIPCI %s cannot read PCI configuration: %s\n",
 		       efi_handle_name ( device ), strerror ( rc ) );
diff --git a/src/tests/settings_test.c b/src/tests/settings_test.c
index 89203d42..828901b0 100644
--- a/src/tests/settings_test.c
+++ b/src/tests/settings_test.c
@@ -422,7 +422,9 @@ static void settings_test_exec ( void ) {
 
 	/* "busdevfn" setting type (no store capability) */
 	fetchf_ok ( &test_settings, &test_busdevfn_setting,
-		    RAW ( 0x03, 0x45 ), "03:08.5" );
+		    RAW ( 0x03, 0x45 ), "0000:03:08.5" );
+	fetchf_ok ( &test_settings, &test_busdevfn_setting,
+		    RAW ( 0x00, 0x02, 0x0a, 0x21 ), "0002:0a:04.1" );
 
 	/* Clear and unregister test settings block */
 	clear_settings ( &test_settings );