linux-kernel - [PATCH v3] cxl/port: Fix target list setup for multiple decoders sharing the same dport

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Message-ID: <20260108101324.509667-1-rrichter@amd.com>
Date: Thu, 8 Jan 2026 11:13:23 +0100
From: Robert Richter <rrichter@....com>
To: Davidlohr Bueso <dave@...olabs.net>, Jonathan Cameron
	<jonathan.cameron@...wei.com>, Dave Jiang <dave.jiang@...el.com>, "Alison
 Schofield" <alison.schofield@...el.com>, Vishal Verma
	<vishal.l.verma@...el.com>, Ira Weiny <ira.weiny@...el.com>, Dan Williams
	<dan.j.williams@...el.com>
CC: Robert Richter <rrichter@....com>, <linux-cxl@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: [PATCH v3] cxl/port: Fix target list setup for multiple decoders sharing the same dport

If a switch port has more than one decoder that is using the same
downstream port, the enumeration of the target lists may fail with:

 # dmesg | grep target.list
 update_decoder_targets: cxl decoder1.0: dport3 found in target list, index 3
 update_decoder_targets: cxl decoder1.0: dport2 found in target list, index 2
 update_decoder_targets: cxl decoder1.0: dport0 found in target list, index 0
 update_decoder_targets: cxl decoder2.0: dport3 found in target list, index 1
 update_decoder_targets: cxl decoder4.0: dport3 found in target list, index 1
 cxl_mem mem6: failed to find endpoint12:0000:00:01.4 in target list of decoder2.1
 cxl_mem mem8: failed to find endpoint13:0000:20:01.4 in target list of decoder4.1

The case, that the same downstream port can be used in multiple target
lists, is allowed and possible.

Fix the update of the target list. Enumerate all children of the
switch port and do not stop the iteration after the first matching
target was found.

With the fix applied:

 # dmesg | grep target.list
 update_decoder_targets: cxl decoder1.0: dport2 found in target list, index 2
 update_decoder_targets: cxl decoder1.0: dport0 found in target list, index 0
 update_decoder_targets: cxl decoder1.0: dport3 found in target list, index 3
 update_decoder_targets: cxl decoder2.0: dport3 found in target list, index 1
 update_decoder_targets: cxl decoder2.1: dport3 found in target list, index 1
 update_decoder_targets: cxl decoder4.0: dport3 found in target list, index 1
 update_decoder_targets: cxl decoder4.1: dport3 found in target list, index 1

Analyzing the conditions when this happens:

1) A dport is shared by multiple decoders.

2) The decoders have interleaving configured (ways > 1).

The configuration above has the following hierarchy details (fixed
version):

 root0
 |_
 | |
 | decoder0.1
 | ways: 2
 | target_list: 0,1
 |_______________________________________
 |                                       |
 | dport0                                | dport1
 |                                       |
 port2                                   port4
 |                                       |
 |___________________                    |_____________________
 | |                 |                   | |                   |
 | decoder2.0        decoder2.1          | decoder4.0          decoder4.1
 | ways: 2           ways: 2             | ways: 2             ways: 2
 | target_list: 2,3  target_list: 2,3    | target_list: 2,3    target_list: 2,3
 |___________________                    |___________________
 |                   |                   |                   |
 | dport2            | dport3            | dport2            | dport3
 |                   |                   |                   |
 endpoint7           endpoint12          endpoint9           endpoint13
 |_                  |_                  |_                  |_
 | |                 | |                 | |                 | |
 | decoder7.0        | decoder12.0       | decoder9.0        | decoder13.0
 | decoder7.2        | decoder12.2       | decoder9.2        | decoder13.2
 |                   |                   |                   |
 mem3                mem5                mem6                mem8

Note: Device numbers vary for every boot.

Current kernel fails to enumerate endpoint12 and endpoint13 as the
target list is not updated for the second decoder.

Fixes: 4f06d81e7c6a ("cxl: Defer dport allocation for switch ports")
Reviewed-by: Dave Jiang <dave.jiang@...el.com>
Reviewed-by: Alison Schofield <alison.schofield@...el.com>
Signed-off-by: Robert Richter <rrichter@....com>
---
v2:
 * updated sob-chain,
 * added fixes tag (Dave).
---
 drivers/cxl/core/port.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
index fef3aa0c6680..3310dbfae9d6 100644
--- a/drivers/cxl/core/port.c
+++ b/drivers/cxl/core/port.c
@@ -1590,7 +1590,7 @@ static int update_decoder_targets(struct device *dev, void *data)
 			cxlsd->target[i] = dport;
 			dev_dbg(dev, "dport%d found in target list, index %d\n",
 				dport->port_id, i);
-			return 1;
+			return 0;
 		}
 	}
 

base-commit: 88c72bab77aaf389beccf762e112828253ca0564
prerequisite-patch-id: f44102a7b095afa1588a5cac012ec2e0d852c021
-- 
2.47.3