1 files changed, 54 insertions, 17 deletions

diff --git a/sys/dev/pci/vga_pci.c b/sys/dev/pci/vga_pci.c
index d7ff20f..c64037f 100644
--- a/sys/dev/pci/vga_pci.c
+++ b/sys/dev/pci/vga_pci.c
@@ -81,16 +81,58 @@ SYSCTL_INT(_hw_pci, OID_AUTO, default_vgapci_unit, CTLFLAG_RDTUN,
 int
 vga_pci_is_boot_display(device_t dev)
 {
+	int unit;
+	device_t pcib;
+	uint16_t config;
+
+	/* Check that the given device is a video card */
+	if ((pci_get_class(dev) != PCIC_DISPLAY &&
+	    (pci_get_class(dev) != PCIC_OLD ||
+	     pci_get_subclass(dev) != PCIS_OLD_VGA)))
+		return (0);
+
+	unit = device_get_unit(dev);
+
+	if (vga_pci_default_unit >= 0) {
+		/*
+		 * The boot display device was determined by a previous
+		 * call to this function, or the user forced it using
+		 * the hw.pci.default_vgapci_unit tunable.
+		 */
+		return (vga_pci_default_unit == unit);
+	}
 
 	/*
-	 * Return true if the given device is the default display used
-	 * at boot time.
+	 * The primary video card used as a boot display must have the
+	 * "I/O" and "Memory Address Space Decoding" bits set in its
+	 * Command register.
+	 *
+	 * Furthermore, if the card is attached to a bridge, instead of
+	 * the root PCI bus, the bridge must have the "VGA Enable" bit
+	 * set in its Control register.
 	 */
-	return (
-	    (pci_get_class(dev) == PCIC_DISPLAY ||
-	     (pci_get_class(dev) == PCIC_OLD &&
-	      pci_get_subclass(dev) == PCIS_OLD_VGA)) &&
-	    device_get_unit(dev) == vga_pci_default_unit);
+
+	pcib = device_get_parent(device_get_parent(dev));
+	if (device_get_devclass(device_get_parent(pcib)) ==
+	    devclass_find("pci")) {
+		/*
+		 * The parent bridge is a PCI-to-PCI bridge: check the
+		 * value of the "VGA Enable" bit.
+		 */
+		config = pci_read_config(pcib, PCIR_BRIDGECTL_1, 2);
+		if ((config & PCIB_BCR_VGA_ENABLE) == 0)
+			return (0);
+	}
+
+	config = pci_read_config(dev, PCIR_COMMAND, 2);
+	if ((config & (PCIM_CMD_PORTEN | PCIM_CMD_MEMEN)) == 0)
+		return (0);
+
+	/* This video card is the boot display: record its unit number. */
+	vga_pci_default_unit = unit;
+	device_set_flags(dev, 1);
+
+	return (1);
 }
 
 void *
@@ -159,9 +201,6 @@ vga_pci_unmap_bios(device_t dev, void *bios)
 static int
 vga_pci_probe(device_t dev)
 {
-	device_t bdev;
-	int unit;
-	uint16_t bctl;
 
 	switch (pci_get_class(dev)) {
 	case PCIC_DISPLAY:
@@ -175,13 +214,7 @@ vga_pci_probe(device_t dev)
 	}
 
 	/* Probe default display. */
-	unit = device_get_unit(dev);
-	bdev = device_get_parent(device_get_parent(dev));
-	bctl = pci_read_config(bdev, PCIR_BRIDGECTL_1, 2);
-	if (vga_pci_default_unit < 0 && (bctl & PCIB_BCR_VGA_ENABLE) != 0)
-		vga_pci_default_unit = unit;
-	if (vga_pci_default_unit == unit)
-		device_set_flags(dev, 1);
+	vga_pci_is_boot_display(dev);
 
 	device_set_desc(dev, "VGA-compatible display");
 	return (BUS_PROBE_GENERIC);
@@ -197,6 +230,10 @@ vga_pci_attach(device_t dev)
 	device_add_child(dev, "drm", -1);
 	device_add_child(dev, "drmn", -1);
 	bus_generic_attach(dev);
+
+	if (vga_pci_is_boot_display(dev))
+		device_printf(dev, "Boot video device\n");
+
 	return (0);
 }