Re: [PATCH] PCI: Allocate maximum available buses to help extending the daisy chain

[Maciej W. Rozycki]

On Fri, 18 Aug 2023, Mika Westerberg wrote:

> > > > > Link: https://bugzilla.kernel.org/show_bug.cgi?id=216000
> > > Did you get confirmation that this actually solves the issue?
> > I've tested this on my setup, it is resolving the issue.
> 
> Right, but it would be good to get confirmation from the person who
> reported the issue that this actually helps. There is nothing in the
> bugzilla whether the patch worked or not.

 If you do change the defaults, then please don't forget to update 
Documentation/admin-guide/kernel-parameters.txt in the same commit 
accordingly for `hpbussize=nn', etc.

 NB it seems a common problem with vendor firmware failing to assign a 
reasonable quantity of downstream buses for hot-plug ports.  E.g. with my 
production laptop back from 2018 a single-device ExpressCard option, such 
as a PCIe serial port works just fine with hot-plug, however if I hot-plug 
a whole bus hierarchy in an external enclosure, then the system runs out 
of buses at the first PCIe switch (unless I use `hpbussize=nn', etc.).

  Maciej