linux-kernel - Re: [PATCH] cxl/hdm: allow zero sized committed decoders

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Message-ID: <aN_cUPzzwUy-s36n@gourry-fedora-PF4VCD3F>
Date: Fri, 3 Oct 2025 10:23:12 -0400
From: Gregory Price <gourry@...rry.net>
To: Vishal Aslot <vaslot@...dia.com>
Cc: Dave Jiang <dave.jiang@...el.com>, Davidlohr Bueso <dave@...olabs.net>,
	Jonathan Cameron <jonathan.cameron@...wei.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>,
	Li Ming <ming.li@...omail.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Dan Carpenter <dan.carpenter@...aro.org>,
	Zijun Hu <zijun.hu@....qualcomm.com>,
	"linux-cxl@...r.kernel.org" <linux-cxl@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cxl/hdm: allow zero sized committed decoders

On Fri, Oct 03, 2025 at 01:03:16AM +0000, Vishal Aslot wrote:
> > ________________________________________
> > From: Dave Jiang <dave.jiang@...el.com>
> > Sent: Thursday, October 2, 2025 10:32 AM
> > To: Gregory Price; Vishal Aslot
> > Cc: Davidlohr Bueso; Jonathan Cameron; Alison Schofield; Vishal Verma; Ira Weiny; Dan Williams; Li Ming; Peter Zijlstra; Dan Carpenter; Zijun Hu; linux-cxl@...r.kernel.org; linux-kernel@...r.kernel.org
> > Subject: Re: [PATCH] cxl/hdm: allow zero sized committed decoders
> > 
> > External email: Use caution opening links or attachments
> > 
> > 
> > On 10/1/25 10:48 PM, Gregory Price wrote:
> >> On Wed, Oct 01, 2025 at 08:37:26PM +0000, Vishal Aslot wrote:
> >>> @@ -1210,6 +1210,11 @@ int devm_cxl_enumerate_decoders(struct cxl_hdm *cxlhdm,
> >>>                 rc = init_hdm_decoder(port, cxld, target_map, hdm, i,
> >>>                                       &dpa_base, info);
> >>>                 if (rc) {
> >>> +                       if (rc == -ENOSPC) {
> >>> +                               put_device(&cxld->dev);
> >>> +                               rc = 0;
> >>> +                               continue;
> >>> +                       }
> >>
> >> How do you suggest actually testing this? I briefly poked at this in
> >> QEMU trying to commit decoders, but i found myself incapable of
> >> exercising this path.
> 
> I tested it locally with our BIOS (UEFI) where we commit and lock all decoders and
> all except decoder 0 are zero-sized.
> 

Ahhh, so are you saying that you will only ever observe the following
(as an example)

endpoint decoders...
decoder2.0   ->  available and can be programmed
decoder2.1   ->  size=0, locked
...
decoder2.N   ->  size=0, locked

or are you suggesting the following is valid:

decoder2.0   ->  size=0, locked
decoder2.1   ->  available and can be programmed
...
decoder2.N   ->  available and can be programmed

~Gregory