Re: [PATCH v14 2/8] cxl/mem: Read dynamic capacity configuration from the device

[Jonathan Cameron <jic23@kernel.org>]

On Fri, 18 Sep 2026 13:30:11 -0700
Anisa Su <anisa.su887@gmail.com> wrote:

> From: Ira Weiny <iweiny@kernel.org>
> 
> Devices which support Dynamic Capacity (DC) are configured
> via mailbox commands. CXL r4.0 section 9.13.3 describes the use of
> the Get DC Configuration command in order to obtain DCD partition
> characteristics.

Wrap has ended up a tiny bit uneven after edits.  I'd rewrap whole commit
to 75 chars if you happen to respin for other reasons.

> 
> Implement the DC mailbox commands as specified in CXL 4.0 section
> 8.2.10.9.9 (opcodes 48XXh) to read and store the DCD configuration
> information. Disable DCD if an invalid configuration is found.
> 
> Initial enablement for Linux only supports one dynamic capacity
> partition. Read all the partitions the device reports but validate
> only the first, and configure it as 'dynamic ram 1'.
> 
> The specification requires that volatile capacity starts at DPA 0 and pmem
> starts at the DPA immediately following it, but DC partitions only need
> to be 256MB aligned according to CXL r4.0 section 8.2.10.9.9.1 Table 8-347.
> So a device could leave a gap between ram/pmem (static) capacity and its first
> DC partition, or between one DC partition and the next.
> 
> However, Linux chooses not to support gaps between static and dynamic
> capacity, and requires the first DC partition to begin at the DPA
> immediately following static capacity.
> 
> Based on an original patch by Navneet Singh.
> 
> Signed-off-by: Ira Weiny <iweiny@kernel.org>
> Co-developed-by: Anisa Su <anisa.su@samsung.com>
> Signed-off-by: Anisa Su <anisa.su@samsung.com>
> Tested-by: Wonjae Lee <wj28.lee@samsung.com>
> Tested-by: Junhee Park <jh9934.park@samsung.com>
> Tested-by: Heesoo Kim <habil.kim@samsung.com>
> Reviewed-by: Alison Schofield <alison.schofield@intel.com>
> 

Reviewed-by: Jonathan Cameron <jonathan.cameron@oss.qualcomm.com>


A personal aim of successfully giving the most trivial feedback ever
is achieved.  See below.



> diff --git a/drivers/cxl/core/memdev.c b/drivers/cxl/core/memdev.c
> index b3419df586b9..15df8db314d9 100644
> --- a/drivers/cxl/core/memdev.c
> +++ b/drivers/cxl/core/memdev.c
> @@ -643,6 +643,54 @@ int cxl_mem_dpa_fetch(struct cxl_memdev_state *mds, struct cxl_dpa_info *info)
>  }
>  EXPORT_SYMBOL_NS_GPL(cxl_mem_dpa_fetch, "CXL");
>  
> +int cxl_configure_dcd(struct cxl_memdev_state *mds, struct cxl_dpa_info *info)
> +{
> +	struct cxl_dc_partition_info dc_info = { };
> +	struct device *dev = mds->cxlds.dev;
> +	u64 total;
> +	int rc;
> +
> +	if (!mds->cxlds.media_ready)
> +		return 0;
> +
> +	rc = cxl_dev_dc_identify(&mds->cxlds.cxl_mbox, &dc_info);
> +	if (rc) {
> +		dev_warn(dev,
> +			 "Failed to read Dynamic Capacity config: %d\n", rc);
> +		return rc;
> +	}
> +
> +	if (dc_info.start < info->size) {
> +		dev_err(dev,
> +			"DC partition 0 base %#llx overlaps static capacity ending at %#llx\n",
> +			dc_info.start, info->size);
> +		return -EINVAL;
> +	}
> +
> +	/* A gap between static capacity and the DC partition is not supported */
> +	if (dc_info.start > info->size) {
> +		dev_warn(dev,
> +			 "DC partition 0 base %#llx leaves a gap from static capacity ending at %#llx\n",
> +			 dc_info.start, info->size);
> +		return -EOPNOTSUPP;
> +	}
> +
> +	if (check_add_overflow(info->size, dc_info.size, &total)) {
> +		dev_err(dev,
> +			"DC partition 0 size %#llx overflows DPA space ending at %#llx\n",
> +			dc_info.size, info->size);
> +		return -EINVAL;
> +	}
> +
> +	info->size = total;
> +	dev_dbg(dev, "Adding dynamic ram partition 1; %#llx size %#llx\n",
> +		dc_info.start, dc_info.size);
> +	add_part(info, dc_info.start, dc_info.size, CXL_PARTMODE_DYNAMIC_RAM_1);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_NS_GPL(cxl_configure_dcd, "CXL");
> +
>  
It is already the case that there is a double line here which is not
common in this file. I have no idea why it is here!
If you happen to respin maybe drop it?

>  /**
>   * cxl_set_capacity: initialize dpa by a driver without a mailbox.