[PATCH v1] cxl/port: Fix target list setup for multiple decoders sharing the same dport

Robert Richter
2026-01-07T10:04:23Z

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.

Signed-off-by: Robert Richter <rrichter@amd.com>
---
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: a92b04b164c158c7f0f0dcde957bf5c02ffb3918
--
2.47.3