linux-kernel - Re: [PATCH 09/26] cxl/region: Add Dynamic Capacity CXL region support

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Date: Tue, 9 Apr 2024 21:35:40 -0700
From: Ira Weiny <ira.weiny@...el.com>
To: Dave Jiang <dave.jiang@...el.com>, <ira.weiny@...el.com>, Fan Ni
	<fan.ni@...sung.com>, Jonathan Cameron <Jonathan.Cameron@...wei.com>, Navneet
 Singh <navneet.singh@...el.com>
CC: Dan Williams <dan.j.williams@...el.com>, Davidlohr Bueso
	<dave@...olabs.net>, Alison Schofield <alison.schofield@...el.com>, "Vishal
 Verma" <vishal.l.verma@...el.com>, <linux-btrfs@...r.kernel.org>,
	<linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 09/26] cxl/region: Add Dynamic Capacity CXL region support

Dave Jiang wrote:
> 
> 
> On 3/24/24 4:18 PM, ira.weiny@...el.com wrote:
> > From: Navneet Singh <navneet.singh@...el.com>
> > 

[snip]

> >  
> > -What:		/sys/bus/cxl/devices/decoderX.Y/create_{pmem,ram}_region
> > -Date:		May, 2022, January, 2023
> > -KernelVersion:	v6.0 (pmem), v6.3 (ram)
> > +What:		/sys/bus/cxl/devices/decoderX.Y/create_{pmem,ram,dc}_region
> > +Date:		May, 2022, January, 2023, June 2024
> > +KernelVersion:	v6.0 (pmem), v6.3 (ram), v6.10 (dc)
> >  Contact:	linux-cxl@...r.kernel.org
> >  Description:
> >  		(RW) Write a string in the form 'regionZ' to start the process
> > -		of defining a new persistent, or volatile memory region
> > -		(interleave-set) within the decode range bounded by root decoder
> > -		'decoderX.Y'. The value written must match the current value
> > -		returned from reading this attribute. An atomic compare exchange
> > -		operation is done on write to assign the requested id to a
> > -		region and allocate the region-id for the next creation attempt.
> > -		EBUSY is returned if the region name written does not match the
> > -		current cached value.
> > +		of defining a new persistent, volatile, or Dynamic Capacity
> > +		(DC) memory region (interleave-set) within the decode range
> > +		bounded by root decoder 'decoderX.Y'. The value written must
> > +		match the current value returned from reading this attribute.
> > +		An atomic compare exchange operation is done on write to assign
> > +		the requested id to a region and allocate the region-id for the
> > +		next creation attempt.  EBUSY is returned if the region name
> 
> -EBUSY?
>

To match the other documentation I would say no.  The other docs show
ENXIO/EBUSY/EINVAL without the negative indicator.


[snip]

> > diff --git a/drivers/dax/cxl.c b/drivers/dax/cxl.c
> > index c696837ab23c..415d03fbf9b6 100644
> > --- a/drivers/dax/cxl.c
> > +++ b/drivers/dax/cxl.c
> > @@ -13,19 +13,30 @@ static int cxl_dax_region_probe(struct device *dev)
> >  	struct cxl_region *cxlr = cxlr_dax->cxlr;
> >  	struct dax_region *dax_region;
> >  	struct dev_dax_data data;
> > +	resource_size_t dev_size;
> > +	unsigned long flags;
> >  
> >  	if (nid == NUMA_NO_NODE)
> >  		nid = memory_add_physaddr_to_nid(cxlr_dax->hpa_range.start);
> >  
> > +	flags = IORESOURCE_DAX_KMEM;
> > +	if (cxlr->mode == CXL_REGION_DC)
> > +		flags |= IORESOURCE_DAX_SPARSE_CAP;
> > +
> >  	dax_region = alloc_dax_region(dev, cxlr->id, &cxlr_dax->hpa_range, nid,
> > -				      PMD_SIZE, IORESOURCE_DAX_KMEM);
> > +				      PMD_SIZE, flags);
> >  	if (!dax_region)
> >  		return -ENOMEM;
> >  
> > +	dev_size = range_len(&cxlr_dax->hpa_range);
> > +	/* Add empty seed dax device */
> > +	if (cxlr->mode == CXL_REGION_DC)
> > +		dev_size = 0;
> 
> Nit. Just do if/else so dev_size isn't set twice if mode is DC.

Ok yea.

Ira