linux-kernel - Re: [RFC PATCH 18/20] cxl/pmem: Add support of cxl lsa 2.1 support in cxl pmem

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Message-ID: <700072760.81752909483184.JavaMail.epsvc@epcpadp2new>
Date: Fri, 18 Jul 2025 18:21:48 +0530
From: Neeraj Kumar <s.neeraj@...sung.com>
To: Dave Jiang <dave.jiang@...el.com>
Cc: dan.j.williams@...el.com, dave@...olabs.net,
	jonathan.cameron@...wei.com, alison.schofield@...el.com,
	vishal.l.verma@...el.com, ira.weiny@...el.com, a.manzanares@...sung.com,
	nifan.cxl@...il.com, anisa.su@...sung.com, vishak.g@...sung.com,
	krish.reddy@...sung.com, arun.george@...sung.com, alok.rathore@...sung.com,
	neeraj.kernel@...il.com, linux-kernel@...r.kernel.org,
	linux-cxl@...r.kernel.org, nvdimm@...ts.linux.dev, gost.dev@...sung.com,
	cpgs@...sung.com
Subject: Re: [RFC PATCH 18/20] cxl/pmem: Add support of cxl lsa 2.1 support
 in cxl pmem

On 10/07/25 10:18AM, Dave Jiang wrote:
>
>
>On 6/17/25 5:39 AM, Neeraj Kumar wrote:
>> Add support of cxl lsa 2.1 using NDD_CXL_LABEL flag. It also creates cxl
>> region based on region information parsed from LSA.
>>
>> Signed-off-by: Neeraj Kumar <s.neeraj@...sung.com>
>> ---
>>  drivers/cxl/pmem.c | 59 ++++++++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 59 insertions(+)
>>
>> diff --git a/drivers/cxl/pmem.c b/drivers/cxl/pmem.c
>> index ffcebb8d382f..2733d79b32d5 100644
>> --- a/drivers/cxl/pmem.c
>> +++ b/drivers/cxl/pmem.c
>> @@ -58,6 +58,63 @@ static const struct attribute_group *cxl_dimm_attribute_groups[] = {
>>  	NULL
>>  };
>>
>> +static int match_ep_decoder(struct device *dev, void *data)
>> +{
>> +	struct cxl_decoder *cxld = to_cxl_decoder(dev);
>> +
>> +	if (!cxld->region)
>> +		return 1;
>> +	else
>> +		return 0;
>> +}
>
>return !cxld->region;
>

Thanks, I will fix it in next patch-set

>
>> +
>> +static struct cxl_decoder *cxl_find_free_decoder(struct cxl_port *port)
>> +{
>> +	struct device *dev;
>> +
>> +	dev = device_find_child(&port->dev, NULL, match_ep_decoder);
>> +	if (!dev)
>> +		return NULL;
>> +
>> +	return to_cxl_decoder(dev);
>> +}
>> +
>> +static int create_pmem_region(struct nvdimm *nvdimm)
>> +{
>> +	struct cxl_nvdimm *cxl_nvd;
>> +	struct cxl_memdev *cxlmd;
>> +	struct cxl_nvdimm_bridge *cxl_nvb;
>> +	struct cxl_pmem_region_params *params;
>> +	struct cxl_root_decoder *cxlrd;
>> +	struct cxl_decoder *cxld;
>> +	struct cxl_region *cxlr;
>> +
>
>probably need a lockdep_assert_held(&cxl_region_rwsem).
>

Thanks Dave, Sure i will fix it with V2

>> +	if (!nvdimm)
>> +		return -ENOTTY;
>
>-ENODEV?

Sure I will fix it with V2

>
>> +
>> +	if (!nvdimm_has_cxl_region(nvdimm))
>> +		return 0;
>> +
>> +	cxl_nvd = nvdimm_provider_data(nvdimm);
>> +	params = nvdimm_get_cxl_region_param(nvdimm);
>> +	cxlmd = cxl_nvd->cxlmd;
>> +	cxl_nvb = cxlmd->cxl_nvb;
>> +	cxlrd = cxlmd->cxlrd;
>> +
>> +	/* FIXME: Limitation: Region creation only when interleave way == 1 */
>> +	if (params->nlabel == 1) {
>> +		cxld = cxl_find_free_decoder(cxlmd->endpoint);
>> +		cxlr = cxl_create_pmem_region(cxlrd, cxld, params,
>> +				atomic_read(&cxlrd->region_id));
>> +		if (IS_ERR(cxlr))
>> +			dev_dbg(&cxlmd->dev, "Region Creation failed\n");
>
>return PTR_ERR(cxlr); ?
>

Thanks, I will fix it in next patch-set

>> +	} else {
>> +		dev_dbg(&cxlmd->dev, "Region Creation is not supported with iw > 1\n");
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>>  static int cxl_nvdimm_probe(struct device *dev)
>>  {
>>  	struct cxl_nvdimm *cxl_nvd = to_cxl_nvdimm(dev);
>> @@ -74,6 +131,7 @@ static int cxl_nvdimm_probe(struct device *dev)
>>  		return rc;
>>
>>  	set_bit(NDD_LABELING, &flags);
>> +	set_bit(NDD_CXL_LABEL, &flags);
>
>Ok here's the NDD_CXL_LABEL set. I think the driver should be probing the label index block and retrieve the label version and determine how to support from there instead of hard coding a flag.

Hi Dave,

We actually write label index information into LSA during namespace/region label updation.
During that time we update its major/minor.

So during first time updation of LSA we must need some way to inform nvdimm about LSA versioning.


Regards,
Neeraj