Re: [BUG] Root port fails to match with port driver on non-RCH topology

[Gregory Price <gregory.price@memverge.com>]

On Thu, Jun 15, 2023 at 02:51:13PM -0400, Gregory Price wrote:
> On Thu, Jun 15, 2023 at 02:46:13PM -0400, Gregory Price wrote:
> > On Thu, Jun 15, 2023 at 12:16:05PM -0400, Gregory Price wrote:
> > follow up with more context, there is a subsequent error on
> > cxl_port_probe which causes dev->driver to remain NULL.
> > 
> > 
> > [   15.561313] cxl_mem mem0: CXL port topology root0 not enabled
> > [   15.561315] cxl_mem mem0: call_driver_probe failed
> 
> wrong prints here, this should have read:
> 
> [   15.549316] cxl root0: driver set to cxl_port
> [   15.549732] cxl_port root0: call_driver_probe failed
> 
> I confirmed that call_driver_probe sinks down to a call to
> cxl_port_probe and that is failing on cxl_port_probe(root0).
> 
> Rest of the commentary below is accurate.
> 


so cxl_switch_port_probe fails on this stack:

- cxl_switch_port_probe
  - devm_cxl_port_enumerate_dports
    - cxl_port_to_pci_bus

int devm_cxl_port_enumerate_dports(struct cxl_port *port)
{
        struct pci_bus *bus = cxl_port_to_pci_bus(port);
        struct cxl_walk_context ctx;
        int type;

        if (!bus)
                return -ENXIO;
...
}

struct pci_bus *cxl_port_to_pci_bus(struct cxl_port *port)
{
    /* There is no pci_bus associated with a CXL platform-root port */
    if (is_cxl_root(port))
        return NULL;
...
}


I presume then that for the root port, we should just return 0 to note
success?  The rest of the devices should register themselves correctly
with the root as they're iterated over - i think?

What I can't figure out is why this doesn't happen on QEMU, which also
presents a similar topology.

Still not sure what is correct vs incorrect here, will need to dig
around in the spec and system settings unless someone has an idea.

~Gregory