linux-kernel - Re: [PATCH v2] cxl/hdm: allow zero sized committed decoders

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Message-ID: <20251004000631.h4vnnpxathjyoez7@offworld>
Date: Fri, 3 Oct 2025 17:06:31 -0700
From: Davidlohr Bueso <dave@...olabs.net>
To: Vishal Aslot <vaslot@...dia.com>
Cc: Dave Jiang <dave.jiang@...el.com>,
	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 v2] cxl/hdm: allow zero sized committed decoders

On Fri, 03 Oct 2025, Vishal Aslot wrote:

>init_hdm_decoder() fails with -ENXIO if a
>committed HDM decoder has zero size.

This can be removed.

>
>The CXL spec permits committing zero sized decoders.

This is enough info, no need for the quote below.
And then add "Linux currently considers them an error".

>See "8.2.4.20.12 Committing Decoder Programming".
>It says,"It is legal for software to program Decoder
>Size to 0 and commit it. Such a decoder will not
>participate in HDM decode."
>
>This patch updates init_hdm_decoder() to return
>-ENOSPC if the decoder is commited with zero-size.

This is not needed in the changelog. Instead the reader
could be enlightened for potential reasons and use
cases of 0 sized decoders.

>The caller leaves the decoder allocated but does not
>add it. It simply continues to the next decoder.

Thanks,
Davidlohr