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

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Message-ID:
 <SN7PR12MB81319DDBBDE50B372F99E9D1BBE5A@SN7PR12MB8131.namprd12.prod.outlook.com>
Date: Sat, 4 Oct 2025 13:34:46 +0000
From: Vishal Aslot <vaslot@...dia.com>
To: Davidlohr Bueso <dave@...olabs.net>
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

> ________________________________________
> From: Davidlohr Bueso <dave@...olabs.net>
> Sent: Friday, October 3, 2025 7:06 PM
> To: Vishal Aslot
> Cc: Dave Jiang; 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 v2] cxl/hdm: allow zero sized committed decoders
> 
> External email: Use caution opening links or attachments
>
>
> 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.

Thank you, Davidlohr, for the review. Much appreciated!
I will remove it in v3.

>
>>
>>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".

Yep, will fix it in v3.

>
>> 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.

Understood. Will update in v3.

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