diff --git a/drivers/pci/rom.c b/drivers/pci/rom.c
index 06663d391b39..b6edb187d160 100644
--- a/drivers/pci/rom.c
+++ b/drivers/pci/rom.c
@@ -35,6 +35,11 @@ int pci_enable_rom(struct pci_dev *pdev)
 	if (res->flags & IORESOURCE_ROM_SHADOW)
 		return 0;
 
+	/*
+	 * Ideally pci_update_resource() would update the ROM BAR address,
+	 * and we would only set the enable bit here.  But apparently some
+	 * devices have buggy ROM BARs that read as zero when disabled.
+	 */
 	pcibios_resource_to_bus(pdev->bus, &region, res);
 	pci_read_config_dword(pdev, pdev->rom_base_reg, &rom_addr);
 	rom_addr &= ~PCI_ROM_ADDRESS_MASK;
diff --git a/drivers/pci/setup-res.c b/drivers/pci/setup-res.c
index 99c9e32775ee..045427336e11 100644
--- a/drivers/pci/setup-res.c
+++ b/drivers/pci/setup-res.c
@@ -72,6 +72,12 @@ static void pci_std_update_resource(struct pci_dev *dev, int resno)
 	if (resno < PCI_ROM_RESOURCE) {
 		reg = PCI_BASE_ADDRESS_0 + 4 * resno;
 	} else if (resno == PCI_ROM_RESOURCE) {
+
+		/*
+		 * Apparently some Matrox devices have ROM BARs that read
+		 * as zero when disabled, so don't update ROM BARs unless
+		 * they're enabled.  See https://lkml.org/lkml/2005/8/30/138.
+		 */
 		if (!(res->flags & IORESOURCE_ROM_ENABLE))
 			return;