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Message-ID: <aWCuOIFIn7ZgBmiW@rric.localdomain>
Date: Fri, 9 Jan 2026 08:28:56 +0100
From: Robert Richter <rrichter@....com>
To: Jonathan Cameron <jonathan.cameron@...wei.com>
Cc: Davidlohr Bueso <dave@...olabs.net>, 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>, linux-cxl@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] cxl/port: Fix target list setup for multiple decoders
sharing the same dport
On Thu, Jan 08, 2026 at 04:08:35PM +0000, Jonathan Cameron wrote:
> On Thu, 8 Jan 2026 11:13:23 +0100
> Robert Richter <rrichter@....com> 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
>
> Hi Robert,
>
> I'm struggling a bit to align this with the above prints. Where is
> decoder1.0 for example? As it's below the root port, I think it's the
> host bridge decoder, which might be this one on your diagram?
I only showed the detail of the setup that was failing. There is
additional a 4-way config (port1/decoder1.0) and (not visible) some
1-way configs. Function update_decoder_targets() is not called for
those.
Thanks for review,
-Robert
>
> Fix makes sense to me.
>
> Jonathan
>
>
> > | 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
>
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