PCI: Add PCI ROM helper for platform-provided ROM images

It turns out that some UEFI systems provide apparently an apparently valid
PCI ROM BAR that turns out to contain garbage, so the attempt in 547b52463
to prefer the ROM from the BAR actually breaks a different set of machines.
As Linus pointed out, the graphics drivers are probably in the best
position to make this judgement, so this basically reverts 547b52463 and
f9a37be0f and adds a new helper function. Followup patches will add support
to nouveau and radeon for probing this ROM source if they can't find a ROM
from some other source.

[bhelgaas: added reporter and bugzilla pointers, s/f4eb5ff05/547b52463]
Reference: https://bugzilla.redhat.com/show_bug.cgi?id=927451
Reference: http://lkml.kernel.org/r/kg69ef$vdb$[e-mail]
Reported-by: Mantas Mikulėnas <[e-mail]>
Reported-by: Chris Murphy <[e-mail]>
Signed-off-by: Matthew Garrett <[e-mail]>
Signed-off-by: Bjorn Helgaas <[e-mail]>

drivers/pci/rom.c

···
 	return min((size_t)(image - rom), size);
 }
 
-static loff_t pci_find_rom(struct pci_dev *pdev, size_t *size)
-{
-	struct resource *res = &pdev->resource[PCI_ROM_RESOURCE];
-	loff_t start;
-
-	/* assign the ROM an address if it doesn't have one */
-	if (res->parent == NULL && pci_assign_resource(pdev, PCI_ROM_RESOURCE))
-		return 0;
-	start = pci_resource_start(pdev, PCI_ROM_RESOURCE);
-	*size = pci_resource_len(pdev, PCI_ROM_RESOURCE);
-
-	if (*size == 0)
-		return 0;
-
-	/* Enable ROM space decodes */
-	if (pci_enable_rom(pdev))
-		return 0;
-
-	return start;
-}
-
 /**
  * pci_map_rom - map a PCI ROM to kernel space
  * @pdev: pointer to pci device struct
···
 void __iomem *pci_map_rom(struct pci_dev *pdev, size_t *size)
 {
 	struct resource *res = &pdev->resource[PCI_ROM_RESOURCE];
-	loff_t start = 0;
+	loff_t start;
 	void __iomem *rom;
 
 	/*
···
 			return (void __iomem *)(unsigned long)
 				pci_resource_start(pdev, PCI_ROM_RESOURCE);
 		} else {
-			start = pci_find_rom(pdev, size);
+			/* assign the ROM an address if it doesn't have one */
+			if (res->parent == NULL &&
+			    pci_assign_resource(pdev,PCI_ROM_RESOURCE))
+				return NULL;
+			start = pci_resource_start(pdev, PCI_ROM_RESOURCE);
+			*size = pci_resource_len(pdev, PCI_ROM_RESOURCE);
+			if (*size == 0)
+				return NULL;
+
+			/* Enable ROM space decodes */
+			if (pci_enable_rom(pdev))
+				return NULL;
 		}
 	}
-
-	/*
-	 * Some devices may provide ROMs via a source other than the BAR
-	 */
-	if (!start && pdev->rom && pdev->romlen) {
-		*size = pdev->romlen;
-		return phys_to_virt(pdev->rom);
-	}
-
-	if (!start)
-		return NULL;
 
 	rom = ioremap(start, *size);
 	if (!rom) {
···
 	if (res->flags & (IORESOURCE_ROM_COPY | IORESOURCE_ROM_BIOS_COPY))
 		return;
 
-	if (!pdev->rom || !pdev->romlen)
-		iounmap(rom);
+	iounmap(rom);
 
 	/* Disable again before continuing, leave enabled if pci=rom */
 	if (!(res->flags & (IORESOURCE_ROM_ENABLE | IORESOURCE_ROM_SHADOW)))
···
 	}
 }
 
+/**
+ * pci_platform_rom - provides a pointer to any ROM image provided by the
+ * platform
+ * @pdev: pointer to pci device struct
+ * @size: pointer to receive size of pci window over ROM
+ */
+void __iomem *pci_platform_rom(struct pci_dev *pdev, size_t *size)
+{
+	if (pdev->rom && pdev->romlen) {
+		*size = pdev->romlen;
+		return phys_to_virt((phys_addr_t)pdev->rom);
+	}
+
+	return NULL;
+}
+
 EXPORT_SYMBOL(pci_map_rom);
 EXPORT_SYMBOL(pci_unmap_rom);
 EXPORT_SYMBOL_GPL(pci_enable_rom);
 EXPORT_SYMBOL_GPL(pci_disable_rom);
+EXPORT_SYMBOL(pci_platform_rom);

include/linux/pci.h

···
 void __iomem __must_check *pci_map_rom(struct pci_dev *pdev, size_t *size);
 void pci_unmap_rom(struct pci_dev *pdev, void __iomem *rom);
 size_t pci_get_rom_size(struct pci_dev *pdev, void __iomem *rom, size_t size);
+void __iomem __must_check *pci_platform_rom(struct pci_dev *pdev, size_t *size);
 
 /* Power management related routines */
 int pci_save_state(struct pci_dev *dev);