video: bcm2708_fb: Disable FB if no displays found

raspberrypi inclusion
category: feature
bugzilla: 50432

--------------------------------

If the firmware hasn't detected a display, the driver would assume
one display was available, but because it had failed to retrieve the
display size it would try to allocate a zero-sized buffer.

Avoid the allocation failure by bailing out early if no display is
found.

See: https://github.com/raspberrypi/linux/issues/3598Signed-off-by: NPhil Elwell <phil@raspberrypi.com>
Signed-off-by: NFang Yafen <yafen@iscas.ac.cn>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

drivers/video/fbdev/bcm2708_fb.c

@@ -1092,10 +1092,9 @@ static int bcm2708_fb_probe(struct platform_device *dev)
 	 * set one display
 	 */
 	if (ret || num_displays == 0) {
-		num_displays = 1;
 		dev_err(&dev->dev,
-			"Unable to determine number of FB's. Assuming 1\n");
-		ret = 0;
+			"Unable to determine number of FBs. Disabling driver.\n");
+		return -ENOENT;
 	} else {
 		fbdev->firmware_supports_multifb = 1;
 	}