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 02:46:13PM -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.

> 
> 
> drivers/cxl/port.c
> static int cxl_port_probe(struct device *dev)
> {
>     struct cxl_port *port = to_cxl_port(dev);
> 
>     if (is_cxl_endpoint(port))
>         return cxl_endpoint_port_probe(port);
>     return cxl_switch_port_probe(port);
> }
> 
> 
> since root is not an endpoint, we probe root as a switch port.
> 
> static int cxl_switch_port_probe(struct cxl_port *port)
> {
>     struct cxl_hdm *cxlhdm;
>     int rc;
> 
>     rc = devm_cxl_port_enumerate_dports(port);
>     if (rc < 0)
>         return rc;
> 
>     if (rc == 1)
>         return devm_cxl_add_passthrough_decoder(port);
> 
>     cxlhdm = devm_cxl_setup_hdm(port, NULL);
>     if (IS_ERR(cxlhdm))
>         return PTR_ERR(cxlhdm);
> 
>     return devm_cxl_enumerate_decoders(cxlhdm, NULL);
> }
> 
> 
> It is likely that dev_cxl_port_enumate_dports is failing, though more
> investigation is needed at this point.
> 
> What I don't know is whether cxl_port_probe is intended to probe the
> root port, or if we should simply be attaching the driver to the root
> port device explicitly rather than going through probe.
> 
> Any guidance would be appreciated.
> 
> ~Gregory