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

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Message-ID:
 <SN7PR12MB81319CD146CC8B4CFD45E62FBBE7A@SN7PR12MB8131.namprd12.prod.outlook.com>
Date: Thu, 2 Oct 2025 01:57:13 +0000
From: Vishal Aslot <vaslot@...dia.com>
To: 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>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cxl/hdm: allow zero sized committed decoders

> ________________________________________
> From: Dave Jiang <dave.jiang@...el.com>
> Sent: Wednesday, October 1, 2025 5:46 PM
> To: Vishal Aslot; 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
> Cc: 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 3:03 PM, Vishal Aslot wrote:
>> Thanks for the quick review, Dave. Yes, forgot to put the commit message. :)
>> About the copyright message. Should I not be updating the year to 2025 in it?
>
> I wouldn't bother unless you are doing massive changes and in that case it would be adding NVidia copyright anyhow for you. Also, typically linux mailing lists prefer responding inline and > not top posting.

Ah, understood. Thanks for the mentoring.

>>
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>> ________________________________________
>> From: Dave Jiang <dave.jiang@...el.com>
>> Sent: Wednesday, October 1, 2025 4:28 PM
>> To: Vishal Aslot; 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
>> Cc: 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 1:37 PM, Vishal Aslot wrote:
>>> Signed-off-by: Vishal Aslot <vaslot@...dia.com>
>>
>> Missing commit log?

Yes, will add one in v2.

>>>
>>> ---
>>>  drivers/cxl/core/hdm.c | 9 +++++++--
>>>  1 file changed, 7 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
>>> index e9e1d555cec6..97a5f27f5b72 100644
>>> --- a/drivers/cxl/core/hdm.c
>>> +++ b/drivers/cxl/core/hdm.c
>>> @@ -1,5 +1,5 @@
>>>  // SPDX-License-Identifier: GPL-2.0-only
>>> -/* Copyright(c) 2022 Intel Corporation. All rights reserved. */
>>> +/* Copyright(c) 2022-2025 Intel Corporation. All rights reserved. */
>>
>> Stray change?

No, it was intentional but I understand that for this small update, I don't need to update copyright info. I'll undo this change in v2.

>>
>>>  #include <linux/seq_file.h>
>>>  #include <linux/device.h>
>>>  #include <linux/delay.h>
>>> @@ -1050,7 +1050,7 @@ static int init_hdm_decoder(struct cxl_port *port, struct cxl_decoder *cxld,
>>>                         dev_warn(&port->dev,
>>>                                  "decoder%d.%d: Committed with zero size\n",
>>>                                  port->id, cxld->id);
>>
>> I wonder if we should make this dev_dbg() now that it's a valid case.

Yes, makes sense. I'll change it to dev_dbg() in v2.

>>
>>> -                       return -ENXIO;
>>> +                       return -ENOSPC;
>>>                 }
>>>                 port->commit_end = cxld->id;
>>>         } else {
>>> @@ -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);
>>
>> Why put_device()? Should we enumerate this decoder instead of pretend it doesn't exist? essentially only a dev_set_name() and device_add()?

That is a good point. The decoder has been committed so it should be accounted for in the OS.
I'll remove put_device() in v2.

>>
>>> +                               rc = 0;
>>
>> Don't think this is needed since the continue will put it at start of the loop where rc gets written by init_hdm_decoder() return value.

Agreed. I was being paranoid. Will remove it in v2. 

>>
>>> +                               continue;
>>> +                       }
>>>                         dev_warn(&port->dev,
>>>                                  "Failed to initialize decoder%d.%d\n",
>>>                                  port->id, i);
>>> --
>>> 2.34.1
>>