radeon: Attempt to use platform-provided ROM image

Some platforms only provide their PCI ROM via a platform-specific interface.
Fall back to attempting that if all other sources fail.
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

drivers/gpu/drm/radeon/radeon_bios.c

@@ -99,6 +99,29 @@ static bool radeon_read_bios(struct radeon_device *rdev)
 	return true;
 }
 
+static bool radeon_read_platform_bios(struct radeon_device *rdev)
+{
+	uint8_t __iomem *bios;
+	size_t size;
+
+	rdev->bios = NULL;
+
+	bios = pci_platform_rom(rdev->pdev, &size);
+	if (!bios) {
+		return false;
+	}
+
+	if (size == 0 || bios[0] != 0x55 || bios[1] != 0xaa) {
+		return false;
+	}
+	rdev->bios = kmemdup(bios, size, GFP_KERNEL);
+	if (rdev->bios == NULL) {
+		return false;
+	}
+
+	return true;
+}
+
 #ifdef CONFIG_ACPI
 /* ATRM is used to get the BIOS on the discrete cards in
  * dual-gpu systems.
@@ -620,6 +643,9 @@ bool radeon_get_bios(struct radeon_device *rdev)
 	if (r == false) {
 		r = radeon_read_disabled_bios(rdev);
 	}
+	if (r == false) {
+		r = radeon_read_platform_bios(rdev);
+	}
 	if (r == false || rdev->bios == NULL) {
 		DRM_ERROR("Unable to locate a BIOS ROM\n");
 		rdev->bios = NULL;