dm: core: Board failing to boot since commit 82de42fa1468 (parent data/probe)

[Wolfgang Wallner]

Hello Simon,

Since commit 82de42fa1468 ("dm: core: Allocate parent data separate from
probing parent") I have trouble booting my board (a custom Apollo Lake design
booted via Coreboot + U-Boot).

I think this is because the function ns16550_serial_ofdata_to_platdata() of
the UART driver noew tries to access the PCI bus before it is probed.
I'm aware of the comment which you have added to pci-uclass.c [1].

So the correct way to fix this would be to adapt the uart driver in ns16550.c?

regards, Wolfgang

Detail information:

As far as I understand the situation the following things happen:
 * My debug UART is probed
 * This triggers a call to ns16550_serial_ofdata_to_platdata()
 * This function tries to read BAR0 from the PCI devices
 * Reading BAR0 returns 0xffffffff, as the PCI bus has not been probed yet
 * The serial driver tries to read from a non-existing register based on this
   invalid BAR0 value and hangs indefinitely.

This is confirmed by the warning which you have introduced a few commits ealier
in commit 4886287ee4f9 ("pci: Print a warning if the bus is accessed before
probing"):

  "dm_pci_get_bdf() PCI: Device 'uart at 18,2' on unprobed bus 'pci'"

[1] "A common cause of this problem is that this function is called in the
ofdata_to_platdata() method of @dev. Accessing the PCI bus in that
method is not allowed, since it has not yet been probed. To fix this,
move that access to the probe() method of @dev instead."