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

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Message-ID: <20250813141218.0000091f@huawei.com>
Date: Wed, 13 Aug 2025 14:12:18 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: 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 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.

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,