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Message-ID: <20260109141913.0000523f@huawei.com>
Date: Fri, 9 Jan 2026 14:19:13 +0000
From: Jonathan Cameron <jonathan.cameron@...wei.com>
To: Robert Richter <rrichter@....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 Fri, 9 Jan 2026 08:28:56 +0100
Robert Richter <rrichter@....com> wrote:
> 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.
>
Ah. Ok.
Reviewed-by: Jonathan Cameron <jonathan.cameron@...wei.com>
> 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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