linux-kernel - Re: [PATCH V2 01/20] nvdimm/label: Introduce NDD_CXL

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Message-ID: <7ff8b51b-7263-4d9c-99f8-1b507cf46262@intel.com>
Date: Fri, 15 Aug 2025 11:06:04 -0700
From: Dave Jiang <dave.jiang@...el.com>
To: Jonathan Cameron <Jonathan.Cameron@...wei.com>,
 Neeraj Kumar <s.neeraj@...sung.com>
Cc: linux-cxl@...r.kernel.org, nvdimm@...ts.linux.dev,
 linux-kernel@...r.kernel.org, gost.dev@...sung.com,
 a.manzanares@...sung.com, vishak.g@...sung.com, neeraj.kernel@...il.com
Subject: Re: [PATCH V2 01/20] nvdimm/label: Introduce NDD_CXL_LABEL flag to
 set cxl label format



On 8/13/25 6:12 AM, Jonathan Cameron wrote:
> On Wed, 30 Jul 2025 17:41:50 +0530
> Neeraj Kumar <s.neeraj@...sung.com> wrote:
> 
>> Prior to LSA 2.1 version, LSA contain only namespace labels. LSA 2.1
>> introduced in CXL 2.0 Spec, which contain region label along with
>> namespace label.
>>
>> NDD_LABELING flag is used for namespace. Introduced NDD_CXL_LABEL
>> flag for region label. Based on these flags nvdimm driver performs
>> operation on namespace label or region label.
>>
>> NDD_CXL_LABEL will be utilized by cxl driver to enable LSA2.1 region
>> label support
>>
>> Accordingly updated label index version
>>
>> Signed-off-by: Neeraj Kumar <s.neeraj@...sung.com>
> Hi Neeraj,
> 
> A few comments inline.
> 
>> diff --git a/drivers/nvdimm/label.c b/drivers/nvdimm/label.c
>> index 04f4a049599a..7a011ee02d79 100644
>> --- a/drivers/nvdimm/label.c
>> +++ b/drivers/nvdimm/label.c
>> @@ -688,11 +688,25 @@ static int nd_label_write_index(struct nvdimm_drvdata *ndd, int index, u32 seq,
>>  		- (unsigned long) to_namespace_index(ndd, 0);
>>  	nsindex->labeloff = __cpu_to_le64(offset);
>>  	nsindex->nslot = __cpu_to_le32(nslot);
>> -	nsindex->major = __cpu_to_le16(1);
>> -	if (sizeof_namespace_label(ndd) < 256)
>> +
>> +	/* Set LSA Label Index Version */
>> +	if (ndd->cxl) {
>> +		/* CXL r3.2 Spec: Table 9-9 Label Index Block Layout */
>> +		nsindex->major = __cpu_to_le16(2);
>>  		nsindex->minor = __cpu_to_le16(1);
>> -	else
>> -		nsindex->minor = __cpu_to_le16(2);
>> +	} else {
>> +		nsindex->major = __cpu_to_le16(1);
>> +		/*
>> +		 * NVDIMM Namespace Specification
>> +		 * Table 2: Namespace Label Index Block Fields
>> +		 */
>> +		if (sizeof_namespace_label(ndd) < 256)
>> +			nsindex->minor = __cpu_to_le16(1);
>> +		else
>> +		 /* UEFI Specification 2.7: Label Index Block Definitions */
> 
> Odd comment alignment. Either put it on the else so
> 		else /* UEFI 2.7: Label Index Block Defintions */
> 
> or indent it an extra tab
> 
> 		else
> 			/* UEFI 2.7: Label Index Block Definitions */
> 			
>> +			nsindex->minor = __cpu_to_le16(2);
>> +	}
>> +
>>  	nsindex->checksum = __cpu_to_le64(0);
>>  	if (flags & ND_NSINDEX_INIT) {
>>  		unsigned long *free = (unsigned long *) nsindex->free;
> 
>> diff --git a/include/linux/libnvdimm.h b/include/linux/libnvdimm.h
>> index e772aae71843..0a55900842c8 100644
>> --- a/include/linux/libnvdimm.h
>> +++ b/include/linux/libnvdimm.h
>> @@ -44,6 +44,9 @@ enum {
>>  	/* dimm provider wants synchronous registration by __nvdimm_create() */
>>  	NDD_REGISTER_SYNC = 8,
>>  
>> +	/* dimm supports region labels (LSA Format 2.1) */
>> +	NDD_CXL_LABEL = 9,
> 
> This enum is 'curious'.  It combined flags from a bunch of different
> flags fields and some stuff that are nothing to do with flags.
> 
> Anyhow, putting that aside I'd either rename it to something like
> NDD_REGION_LABELING (similar to NDD_LABELING that is there for namespace labels
> or just have it a meaning it is LSA Format 2.1 and drop the fact htat
> also means region labels are supported.

I agree. I had a conversation with Dan about it where I mentioned calling it CXL to describe LSA 2.1 just doesn't seem quite right. He also offered up something like NDD_REGION_LABELING instead of NDD_CXL_LABEL. So +1 to this comment.

DJ 

> 
> Combination of a comment that talks about one thing and a definition name
> that doesn't associate with it seems confusing to me.
> 
> Jonathan
> 
> 
>> +
>>  	/* need to set a limit somewhere, but yes, this is likely overkill */
>>  	ND_IOCTL_MAX_BUFLEN = SZ_4M,
>>  	ND_CMD_MAX_ELEM = 5,
> 
>