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Message-ID:
<SN7PR12MB8131F796BAE8B6243E088879BBE7A@SN7PR12MB8131.namprd12.prod.outlook.com>
Date: Fri, 3 Oct 2025 00:59:07 +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: [PATCH v2] cxl/hdm: allow zero sized committed decoders
init_hdm_decoder() fails with -ENXIO if a
committed HDM decoder has zero size.
The CXL spec permits committing zero sized decoders.
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.
The caller leaves the decoder allocated but does not
add it. It simply continues to the next decoder.
Signed-off-by: Vishal Aslot <vaslot@...dia.com>
---
drivers/cxl/core/hdm.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
index e9e1d555cec6..50164fd1b434 100644
--- a/drivers/cxl/core/hdm.c
+++ b/drivers/cxl/core/hdm.c
@@ -1047,10 +1047,10 @@ static int init_hdm_decoder(struct cxl_port *port, struct cxl_decoder *cxld,
}
+ port->commit_end = cxld->id;
+
if (size == 0) {
- dev_warn(&port->dev,
+ dev_dbg(&port->dev,
"decoder%d.%d: Committed with zero size\n",
port->id, cxld->id);
- return -ENXIO;
+ return -ENOSPC;
}
- port->commit_end = cxld->id;
} else {
@@ -1210,6 +1210,9 @@ 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) {
+ continue;
+ }
dev_warn(&port->dev,
"Failed to initialize decoder%d.%d\n",
port->id, i);
--
2.34.1
> ________________________________________
> From: Vishal Aslot <vaslot@...dia.com>
> Sent: Wednesday, October 1, 2025 8:57 PM
> To: Dave Jiang; 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
>
>
>> ________________________________________
>> 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.
>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> ________________________________________
>>> 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
>>>
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