PCI: return error on failure to read PCI ROMs

This patch makes the ROM reading code return an error to user space if
the size of the ROM read is equal to 0.

The patch also emits a warnings if the contents of the ROM are invalid,
and documents the effects of the "enable" file on ROM reading.

Signed-off-by: Timothy S. Nelson <wayland@wayland.id.au>
Acked-by: Alex Villacis-Lasso <a_villacis@palosanto.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
diff --git a/drivers/pci/rom.c b/drivers/pci/rom.c
index 132a781..29cbe47 100644
--- a/drivers/pci/rom.c
+++ b/drivers/pci/rom.c
@@ -63,7 +63,7 @@
  * The PCI window size could be much larger than the
  * actual image size.
  */
-size_t pci_get_rom_size(void __iomem *rom, size_t size)
+size_t pci_get_rom_size(struct pci_dev *pdev, void __iomem *rom, size_t size)
 {
 	void __iomem *image;
 	int last_image;
@@ -72,8 +72,10 @@
 	do {
 		void __iomem *pds;
 		/* Standard PCI ROMs start out with these bytes 55 AA */
-		if (readb(image) != 0x55)
+		if (readb(image) != 0x55) {
+			dev_err(&pdev->dev, "Invalid ROM contents\n");
 			break;
+		}
 		if (readb(image + 1) != 0xAA)
 			break;
 		/* get the PCI data structure and check its signature */
@@ -159,7 +161,7 @@
 	 * size is much larger than the actual size of the ROM.
 	 * True size is important if the ROM is going to be copied.
 	 */
-	*size = pci_get_rom_size(rom, *size);
+	*size = pci_get_rom_size(pdev, rom, *size);
 	return rom;
 }