netdev - Re: [PATCH v12 13/23] cxl: define a driver interface for DPA allocation

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Message-ID: <a0ed9543-dab3-4c56-b128-f3372eb3ce82@intel.com>
Date: Fri, 11 Apr 2025 15:41:13 -0700
From: Dave Jiang <dave.jiang@...el.com>
To: alejandro.lucero-palau@....com, linux-cxl@...r.kernel.org,
 netdev@...r.kernel.org, dan.j.williams@...el.com, edward.cree@....com,
 davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com, edumazet@...gle.com
Cc: Alejandro Lucero <alucerop@....com>,
 Ben Cheatham <benjamin.cheatham@....com>
Subject: Re: [PATCH v12 13/23] cxl: define a driver interface for DPA
 allocation



On 3/31/25 7:45 AM, alejandro.lucero-palau@....com wrote:
> From: Alejandro Lucero <alucerop@....com>
> 
> Region creation involves finding available DPA (device-physical-address)
> capacity to map into HPA (host-physical-address) space. Define an API,
> cxl_request_dpa(), that tries to allocate the DPA memory the driver
> requires to operate. The memory requested should not be bigger than the
> max available HPA obtained previously with cxl_get_hpa_freespace.
> 
> Based on https://lore.kernel.org/linux-cxl/168592158743.1948938.7622563891193802610.stgit@dwillia2-xfh.jf.intel.com/
> 
> Signed-off-by: Alejandro Lucero <alucerop@....com>
> Reviewed-by: Ben Cheatham <benjamin.cheatham@....com>
> ---
>  drivers/cxl/core/hdm.c | 83 ++++++++++++++++++++++++++++++++++++++++++
>  include/cxl/cxl.h      |  5 +++
>  2 files changed, 88 insertions(+)
> 
> diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
> index 70cae4ebf8a4..db6d99e07d45 100644
> --- a/drivers/cxl/core/hdm.c
> +++ b/drivers/cxl/core/hdm.c
> @@ -3,6 +3,7 @@
>  #include <linux/seq_file.h>
>  #include <linux/device.h>
>  #include <linux/delay.h>
> +#include <cxl/cxl.h>
>  
>  #include "cxlmem.h"
>  #include "core.h"
> @@ -572,6 +573,7 @@ int cxl_dpa_free(struct cxl_endpoint_decoder *cxled)
>  	devm_cxl_dpa_release(cxled);
>  	return 0;
>  }
> +EXPORT_SYMBOL_NS_GPL(cxl_dpa_free, "CXL");
>  
>  int cxl_dpa_set_part(struct cxl_endpoint_decoder *cxled,
>  		     enum cxl_partition_mode mode)
> @@ -686,6 +688,87 @@ int cxl_dpa_alloc(struct cxl_endpoint_decoder *cxled, unsigned long long size)
>  	return devm_add_action_or_reset(&port->dev, cxl_dpa_release, cxled);
>  }
>  
> +static int find_free_decoder(struct device *dev, const void *data)
> +{
> +	struct cxl_endpoint_decoder *cxled;
> +	struct cxl_port *port;
> +
> +	if (!is_endpoint_decoder(dev))
> +		return 0;
> +
> +	cxled = to_cxl_endpoint_decoder(dev);
> +	port = cxled_to_port(cxled);
> +
> +	if (cxled->cxld.id != port->hdm_end + 1)
> +		return 0;
> +
> +	return 1;
> +}
> +
> +/**
> + * cxl_request_dpa - search and reserve DPA given input constraints
> + * @cxlmd: memdev with an endpoint port with available decoders
> + * @is_ram: DPA operation mode (ram vs pmem)
> + * @alloc: dpa size required
> + *
> + * Given that a region needs to allocate from limited HPA capacity it
> + * may be the case that a device has more mappable DPA capacity than
> + * available HPA. The expectation is that @alloc is a driver known
> + * value based on the device capacity but it could not be available
> + * due to HPA constraints.
> + *
> + * Returns a pinned cxl_decoder with at least @alloc bytes of capacity
> + * reserved, or an error pointer. The caller is also expected to own the
> + * lifetime of the memdev registration associated with the endpoint to
> + * pin the decoder registered as well.
> + */
> +struct cxl_endpoint_decoder *cxl_request_dpa(struct cxl_memdev *cxlmd,
> +					     bool is_ram,

Why not just pass in 'enum cxl_partition_mode' directly?

DJ

> +					     resource_size_t alloc)
> +{
> +	struct cxl_port *endpoint = cxlmd->endpoint;
> +	struct cxl_endpoint_decoder *cxled;
> +	enum cxl_partition_mode mode;
> +	struct device *cxled_dev;
> +	int rc;
> +
> +	if (!IS_ALIGNED(alloc, SZ_256M))
> +		return ERR_PTR(-EINVAL);
> +
> +	down_read(&cxl_dpa_rwsem);
> +	cxled_dev = device_find_child(&endpoint->dev, NULL, find_free_decoder);
> +	up_read(&cxl_dpa_rwsem);
> +
> +	if (!cxled_dev)
> +		return ERR_PTR(-ENXIO);
> +
> +	cxled = to_cxl_endpoint_decoder(cxled_dev);
> +
> +	if (!cxled) {
> +		rc = -ENODEV;
> +		goto err;
> +	}
> +
> +	if (is_ram)
> +		mode = CXL_PARTMODE_RAM;
> +	else
> +		mode = CXL_PARTMODE_PMEM;
> +
> +	rc = cxl_dpa_set_part(cxled, mode);
> +	if (rc)
> +		goto err;
> +
> +	rc = cxl_dpa_alloc(cxled, alloc);
> +	if (rc)
> +		goto err;
> +
> +	return cxled;
> +err:
> +	put_device(cxled_dev);
> +	return ERR_PTR(rc);
> +}
> +EXPORT_SYMBOL_NS_GPL(cxl_request_dpa, "CXL");
> +
>  static void cxld_set_interleave(struct cxl_decoder *cxld, u32 *ctrl)
>  {
>  	u16 eig;
> diff --git a/include/cxl/cxl.h b/include/cxl/cxl.h
> index a098b4e26980..22061646b147 100644
> --- a/include/cxl/cxl.h
> +++ b/include/cxl/cxl.h
> @@ -7,6 +7,7 @@
>  #include <linux/cdev.h>
>  #include <linux/node.h>
>  #include <linux/ioport.h>
> +#include <linux/range.h>
>  #include <cxl/mailbox.h>
>  
>  /*
> @@ -256,4 +257,8 @@ struct cxl_root_decoder *cxl_get_hpa_freespace(struct cxl_memdev *cxlmd,
>  					       unsigned long flags,
>  					       resource_size_t *max);
>  void cxl_put_root_decoder(struct cxl_root_decoder *cxlrd);
> +struct cxl_endpoint_decoder *cxl_request_dpa(struct cxl_memdev *cxlmd,
> +					     bool is_ram,
> +					     resource_size_t alloc);
> +int cxl_dpa_free(struct cxl_endpoint_decoder *cxled);
>  #endif