Re: [PATCH 1/9] cxl/port: Cleanup handling of the nr_dports 0 -> 1 transition

[<dan.j.williams@intel.com>]

Jonathan Cameron wrote:
> On Wed, 21 Jan 2026 19:33:22 -0800
> Dan Williams <dan.j.williams@intel.com> wrote:
> 
> > There are multiple setup actions that can occur for a switch port after it
> > is known that it has at least one active downstream link. That work is
> > currently split between __devm_cxl_add_dport(), the add_dport() helper, and
> > cxl_port_add_dport() where decoder setup occurs.
> > 
> > Clean this up by moving all @dport object setup responsibilities into
> > add_dport() and all port effects into cxl_port_add_dport().
> > 
> > add_dport() handles taking a reference on @dport->dport_dev, and
> > cxl_port_add_dport() grows the awareness to setup the port component
> > registers. This removes an awkward open-coded xa_erase() from the middle of
> > __devm_cxl_add_dport() and instead tasks cxl_port_add_dport() with calling
> > the common @dport destruction path if anything goes wrong.
> > 
> > After this @port->nr_dports is always the count of @dports in the
> > @port->dports xarray, and cxl_dport_remove() is symmetric with add_dport().
> > With ->nr_dports now reliably tracking the number of dports the use of
> > ida_is_empty() can be dropped. Recall that the ida is only cleared on
> > "release" of decoder objects, and release can be arbitrarily delayed past
> > unregistration.
> 
> Given we only care about nr_dports going to and and from 0, why do
> we need nr_dports at all?  Why not use xa_empty() as the condition.
> 
> Does this now guarantee we don't need the extra nr_dports reset in
> cxl_switch_port_probe()?  That also made me suspicious of something
> funny going on as the count should have dropped to zero if we
> are in state to rebind.
> 
> Other than those this looks good to me and both of those are perhaps
> topics for other patches even if maybe they could be done in here.

True. I had just been assuming that nr_dports was still needed for other
reasons. It turns out that the original need for nr_dports:

    e4f6dfa9ef75 cxl/region: Fix 'distance' calculation with passthrough ports

...was obviated here:

    711442e29f16 cxl/region: Fix passthrough-decoder detection

So, yes, I would be on board with switching to xa_empty() as a follow-on
cleanup.