linux-kernel - Re: [PATCH] cxl/core/port: defer probe when memdev fails to find correct port

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Message-ID: <ZurAiwt7t2WWVrJM@PC2K9PVX.TheFacebook.com>
Date: Wed, 18 Sep 2024 13:59:07 +0200
From: Gregory Price <gourry@...rry.net>
To: Dan Williams <dan.j.williams@...el.com>
Cc: linux-cxl@...r.kernel.org, linux-kernel@...r.kernel.org,
	dave@...olabs.net, jonathan.cameron@...wei.com,
	dave.jiang@...el.com, alison.schofield@...el.com,
	vishal.l.verma@...el.com, ira.weiny@...el.com, rrichter@....com,
	terry.bowman@....com
Subject: Re: [PATCH] cxl/core/port: defer probe when memdev fails to find
 correct port

On Fri, Sep 13, 2024 at 09:32:48PM -0700, Dan Williams wrote:
> Gregory Price wrote:
> > Depending on device/hierarchy readiness, it can be possible for the
> > async probe process to attempt to register an endpoint before the
> > entire port hierarchy is ready.  This currently fails with -ENXIO.
> > 
> > Return -EPROBE_DEFER to try again later automatically (which is
> > what the local comments already say we should do anyway).
> 
> I want to make sure this is not papering over some other issue. Can you
> post the final topology when this works (cxl list -BPET)? My working
> theory is that you have 2 devices that share an intermediate port.
> Otherwise, I am having a hard time understanding why the
> cxl_bus_rescan() in cxl_acpi_probe() does not obviate the explicit
> EPROBE_DEFER.
>

Sorry for the delay

[
  {
    "bus":"root0",
    "provider":"ACPI.CXL",
    "nr_dports":4,
    "dports":[
      {
        "dport":"pci0000:e0",
        "alias":"ACPI0016:00",
        "id":7
      },
      {
        "dport":"pci0000:00",
        "alias":"ACPI0016:01",
        "id":0
      },
      {
        "dport":"pci0000:c0",
        "alias":"ACPI0016:02",
        "id":6
      },
      {
        "dport":"pci0000:20",
        "alias":"ACPI0016:03",
        "id":1
      }
    ],
    "ports:root0":[
      {
        "port":"port1",
        "host":"pci0000:e0",
        "depth":1,
        "decoders_committed":2,
        "nr_dports":4,
        "dports":[
          {
            "dport":"0000:e0:07.2",
            "alias":"device:16",
            "id":114
          },
          {
            "dport":"0000:e0:01.1",
            "alias":"device:02",
            "id":0
          },
          {
            "dport":"0000:e0:01.3",
            "alias":"device:05",
            "id":2
          },
          {
            "dport":"0000:e0:07.1",
            "alias":"device:0d",
            "id":113
          }
        ],
        "endpoints:port1":[
          {
            "endpoint":"endpoint5",
            "host":"mem0",
            "parent_dport":"0000:e0:01.1",
            "depth":2,
            "decoders_committed":1
          }
        ]
      },
      {
        "port":"port3",
        "host":"pci0000:c0",
        "depth":1,
        "decoders_committed":2,
        "nr_dports":1,
        "dports":[
          {
            "dport":"0000:c0:01.1",
            "alias":"device:c3",
            "id":0
          }
        ],
        "endpoints:port3":[
          {
            "endpoint":"endpoint6",
            "host":"mem1",
            "parent_dport":"0000:c0:01.1",
            "depth":2,
            "decoders_committed":1
          }
        ]
      },
      {
        "port":"port2",
        "host":"pci0000:00",
        "depth":1,
        "decoders_committed":0,
        "nr_dports":2,
        "dports":[
          {
            "dport":"0000:00:01.3",
            "alias":"device:55",
            "id":2
          },
          {
            "dport":"0000:00:07.1",
            "alias":"device:5d",
            "id":113
          }
        ]
      },
      {
        "port":"port4",
        "host":"pci0000:20",
        "depth":1,
        "decoders_committed":0,
        "nr_dports":1,
        "dports":[
          {
            "dport":"0000:20:01.1",
            "alias":"device:d0",
            "id":0
          }
        ]
      }
    ]
  }
]
 
> So, devA is dependendent on devB to create a common port, but devA loses
> that race after cxl_bus_rescan() has already run. Then EBPROBE_DEFER is
> the right answer to trigger devA to try again.