On 15/01/2018 10:36, Koen Vandeputte wrote:
> The subordinate value indicates the highest bus number which can be
> reached downstream though a certain device.
>
> Commit a20c7f36bd3d ("PCI: Do not allocate more buses than available in
> parent")
> ensures that downstream devices cannot assign busnumbers higher than the
> upstream device subordinate number, which was indeed illogical.
>
> By default, dw_pcie_setup_rc() inits the Root Complex subordinate to a
> value of 0x01.
>
> Due to this combined with above commit, enumeration stops digging deeper
> downstream as soon as bus num 0x01 has been assigned, which is always
> the case for a bridge device.
>
> This results in all devices behind a bridge bus to remain undetected, as
> these would be connected to bus 0x02 or higher.
>
> Fix this by initializing the RC to a subordinate value of 0xff, which is
> not altering hardware behaviour in any way, but informs probing
> function pci_scan_bridge() later on which reads this value back from
> register.
>
> Following nasty errors during boot are also fixed by this:
>
> [ 0.459145] pci_bus 0000:02: busn_res: can not insert [bus 02-ff]
> under [bus 01] (conflicts with (null) [bus 01])
> ...
> [ 0.464515] pci_bus 0000:03: [bus 03] partially hidden behind bridge
> 0000:01 [bus 01]
> ...
> [ 0.464892] pci_bus 0000:04: [bus 04] partially hidden behind bridge
> 0000:01 [bus 01]
> ...
> [ 0.466488] pci_bus 0000:05: [bus 05] partially hidden behind bridge
> 0000:01 [bus 01]
> [ 0.466506] pci_bus 0000:02: busn_res: [bus 02-ff] end is updated to
> 05
> [ 0.466517] pci_bus 0000:02: busn_res: can not insert [bus 02-05]
> under [bus 01] (conflicts with (null) [bus 01])
> [ 0.466534] pci_bus 0000:02: [bus 02-05] partially hidden behind
> bridge 0000:01 [bus 01]
FWIW, I find that this wrap-around looks ugly :-p
Regards.
