Barebox OF-Overlay Handling

[Marco Felsch]

Hi there,

I have the following problem. My customer is using overlays for
external devices like: display, camera, etc. The current overlay support
is awesome and most of it works out of the box. There is only one
nitpick: If Barebox isn't build with CONFIG_OF_OVERLAY_LIVE enabled many
error's are printed during boot. Those error's are ignored but let the
user assume that something went really bad:

ERROR: of_resolver: __symbols__ missing from base devicetree
ERROR: of_overlay: fragment 30164b88: phandle 0xffffffff not found
ERROR: of_overlay: fragment 30164c84: phandle 0xffffffff not found
ERROR: of_overlay: fragment 3012fb08: phandle 0xffffffff not found
ERROR: of_overlay: fragment 3012fc34: phandle 0xffffffff not found
ERROR: of_overlay: fragment 3012fd60: phandle 0xffffffff not found
ERROR: of_overlay: fragment 3012fe8c: phandle 0xffffffff not found
ERROR: of_overlay: fragment 3012ffb8: phandle 0xffffffff not found
ERROR: of_overlay: fragment 301300e4: phandle 0xffffffff not found
ERROR: of_overlay: fragment 30130210: phandle 0xffffffff not found
ERROR: of_overlay: fragment 3013033c: phandle 0xffffffff not found
ERROR: of_resolver: __symbols__ missing from base devicetree
ERROR: of_overlay: fragment 30130e94: phandle 0xffffffff not found
ERROR: of_overlay: fragment 30130fc4: phandle 0xffffffff not found
ERROR: of_resolver: __symbols__ missing from base devicetree
ERROR: of_overlay: fragment 30131a14: phandle 0xffffffff not found
ERROR: of_overlay: fragment 301342d4: phandle 0xffffffff not found

The of_firmware_load_overlay() calls triggering those errors.
The error's by itself are correct and I don't wanna change them but the
context must be correct by context I mean:

 - barebox-dt on fpga-platform: An FPGA platform needs a barebox
   base devicetree with __symbols__ and those error are correct because
   the firmware manager needs to load the firmware.
 - barebox-dt on non fpga-platform: Those errors are not correct.
   We don't need __symbols__ for the barebox base devicetree.
 - kernel-dt on any platform: Those error's are correct if
   the overlays are using phandles which should be the case most the
   time.

My proposed solution would be a stub like this:

#ifdef CONFIG_OF_OVERLAY_LIVE
int of_firmware_load_overlay(struct device_node *overlay, const char *path);
#else
static inline int of_firmware_load_overlay(struct device_node *overlay, const char *path)
{
       return 0;
}
#endif /* CONFIG_OF_OVERLAY_LIVE */

The disadvantage of this solution is that it can happen to end in a
non-booting device for FPGA platforms using overlays to programm the
bit stream and forget to enable CONFIG_OF_OVERLAY_LIVE because the
kernel tries to access regions not existing.

I've discussed this with Michael in private but we didn't came to a
conclusion. Therefore I'm asking here any input would be helpfull :)

Regards,
  Marco