Re: [PATCH v11 20/22] cxl: Store QTG IDs and related info to the CXL memory device context

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

Gregory Price wrote:
> On Thu, Oct 12, 2023 at 11:55:30AM -0700, Dave Jiang wrote:
> > Once the QTG ID _DSM is executed successfully, the QTG ID is retrieved from
> > the return package. Create a list of entries in the cxl_memdev context and
> > store the QTG ID as qos_class token and the associated DPA range. This
> > information can be exposed to user space via sysfs in order to help region
> > setup for hot-plugged CXL memory devices.
> > 
> > Signed-off-by: Dave Jiang <dave.jiang@intel.com>
> > 
> [... snip ...]
> >  static int cxl_switch_port_probe(struct cxl_port *port)
> >  {
> >  	struct cxl_hdm *cxlhdm;
> > @@ -196,17 +239,22 @@ static int cxl_endpoint_port_probe(struct cxl_port *port)
> >  		rc = cxl_cdat_endpoint_process(port, &dsmas_list);
> >  		if (rc < 0) {
> >  			dev_dbg(&port->dev, "Failed to parse CDAT: %d\n", rc);
> > -		} else {
> > -			rc = cxl_port_perf_data_calculate(port, &dsmas_list);
> > -			if (rc)
> > -				dev_dbg(&port->dev,
> > -					"Failed to do perf coord calculations.\n");
> > +			goto out;
> >  		}
> >  
> > +		rc = cxl_port_perf_data_calculate(port, &dsmas_list);
> > +		if (rc) {
> > +			dev_dbg(&port->dev,
> > +				"Failed to do perf coord calculations.\n");
> > +			goto out;
> > +		}
> > +
> > +		cxl_memdev_set_qos_class(cxlds, &dsmas_list);
> > +out:
> >  		cxl_cdat_dsmas_list_destroy(&dsmas_list);
> >  	}
> >  
> > -	return 0;
> > +	return rc;
> >  }
> 
> This causes existing devices which do not have _DSM implemented to fail
> to map without this QoS extension.  Please consider having the
> cxl_switch_port_probe function return 0 even if the QoS changes here
> fail so that existing expander mapping continues to work.
> 
> I presume future QEMU implementations will have the appropriate _DSM
> acpi field, but older ones do not.

I'll drop that error return for now.