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

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Message-ID: <aOP3Kr3jHLWOydRp@gourry-fedora-PF4VCD3F>
Date: Mon, 6 Oct 2025 13:06:50 -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 Sat, Oct 04, 2025 at 01:49:26PM +0000, Vishal Aslot wrote:
> >>
> >
> > 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
> 
> The first case is what we've got. In our case, the HB has 4 decoders. The end point (a Montage card with single port) has two decoders. For both, we commit & lock all decoders and all decoders except decoder<port>.0 are zero-sized.

If the second case is not supported (I don't think it is), then it's
worth spelling this out.

I don't think either of these cases are relevant for scenarios outside
of the scenario where the host pre-configures the decoders either -
worth spelling that out as well.

Just in the commit log.

~Gregory