linux-kernel - Re: [PATCH RFC v2 08/18] cxl/region: Add Dynamic Capacity CXL region support

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Message-ID: <20230829161948.0000556c@Huawei.com>
Date:   Tue, 29 Aug 2023 16:19:48 +0100
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Ira Weiny <ira.weiny@...el.com>
CC:     Dan Williams <dan.j.williams@...el.com>,
        Navneet Singh <navneet.singh@...el.com>,
        Fan Ni <fan.ni@...sung.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Dave Jiang <dave.jiang@...el.com>,
        Alison Schofield <alison.schofield@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        <linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC v2 08/18] cxl/region: Add Dynamic Capacity CXL
 region support

On Mon, 28 Aug 2023 22:20:59 -0700
Ira Weiny <ira.weiny@...el.com> wrote:

> CXL devices optionally support dynamic capacity.  CXL Regions must be
> configured correctly to access this capacity.  Similar to ram and pmem
> partitions, DC Regions represent different partitions of the DPA space.
> 
> Interleaving is deferred due to the complexity of managing extents on
> multiple devices at the same time.  However, there is nothing which
> directly prevents interleave support at this time.  The check allows
> for early rejection.
> 
> To maintain backwards compatibility with older software, CXL regions
> need a default DAX device to hold the reference for the region until it
> is deleted.
> 
> Add create_dc_region sysfs entry to create DC regions.  Share the logic
> of devm_cxl_add_dax_region() and region_is_system_ram().  Special case
> DC capable CXL regions to create a 0 sized seed DAX device until others
> can be created on dynamic space later.
> 
> Flag dax_regions to indicate 0 capacity available until dax_region
> extents are supported by the region.
> 
> Co-developed-by: Navneet Singh <navneet.singh@...el.com>
> Signed-off-by: Navneet Singh <navneet.singh@...el.com>
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>
> 
LGTM
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>