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Message-ID:
<SN7PR12MB81316FBE4ADDE21FC1F717B0BBE4A@SN7PR12MB8131.namprd12.prod.outlook.com>
Date: Fri, 3 Oct 2025 20:02:05 +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 v2] cxl/hdm: allow zero sized committed decoders
> ________________________________________
> From: Dave Jiang <dave.jiang@...el.com>
> Sent: Friday, October 3, 2025 11:20 AM
> 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 v2] cxl/hdm: allow zero sized committed decoders
>
> External email: Use caution opening links or attachments
>
>
> On 10/2/25 5:59 PM, Vishal Aslot wrote:
>> 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>
>
> Hi Vishal,
> Next time please post the next version of patches as a new thread and not a response to a > previous discussion. It would make lore [1] viewing easier. Thanks!
>
> [1]: https://lore.kernel.org/linux-cxl/aN_cUPzzwUy-s36n@gourry-fedora-PF4VCD3F/T/#t
>
> DJ
Yep, will do. Sorry I should've checked before hand.
>
>> ---
>> 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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