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

Dave Jiang
2026-01-07T18:08:29Z

On 1/7/26 3:03 AM, Robert Richter wrote:
> 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>

Reviewed-by: Dave Jiang <dave.jiang@intel.com>

Can you add a Fixes tag pls?

DJ
> ---
> 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