netdev - Re: [PATCH v12 19/23] cxl: add region flag for precluding a device memory to be used for dax

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Message-ID: <9b7d9ea4-fd7e-4351-82ea-af56b246ff0a@intel.com>
Date: Fri, 11 Apr 2025 16:25:13 -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>, Zhi Wang <zhiw@...dia.com>,
 Jonathan Cameron <Jonathan.Cameron@...wei.com>,
 Ben Cheatham <benjamin.cheatham@....com>
Subject: Re: [PATCH v12 19/23] cxl: add region flag for precluding a device
 memory to be used for dax



On 3/31/25 7:45 AM, alejandro.lucero-palau@....com wrote:
> From: Alejandro Lucero <alucerop@....com>
> 
> By definition a type2 cxl device will use the host managed memory for
> specific functionality, therefore it should not be available to other
> uses. However, a dax interface could be just good enough in some cases.
> 
> Add a flag to a cxl region for specifically state to not create a dax
> device. Allow a Type2 driver to set that flag at region creation time.
> 
> Signed-off-by: Alejandro Lucero <alucerop@....com>
> Reviewed-by: Zhi Wang <zhiw@...dia.com>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> Reviewed-by: Ben Cheatham <benjamin.cheatham@....com>

Reviewed-by: Dave Jiang <dave.jiang@...el.com>
> ---
>  drivers/cxl/core/region.c | 10 +++++++++-
>  drivers/cxl/cxl.h         |  3 +++
>  include/cxl/cxl.h         |  3 ++-
>  3 files changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index f2e1d5719a70..58b68baf2bf3 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -3646,12 +3646,14 @@ __construct_new_region(struct cxl_root_decoder *cxlrd,
>   * @cxlrd: root decoder to allocate HPA
>   * @cxled: endpoint decoder with reserved DPA capacity
>   * @ways: interleave ways required
> + * @no_dax: if true no DAX device should be created
>   *
>   * Returns a fully formed region in the commit state and attached to the
>   * cxl_region driver.
>   */
>  struct cxl_region *cxl_create_region(struct cxl_root_decoder *cxlrd,
> -				     struct cxl_endpoint_decoder *cxled, int ways)
> +				     struct cxl_endpoint_decoder *cxled, int ways,
> +				     bool no_dax)
>  {
>  	struct cxl_region *cxlr;
>  
> @@ -3668,6 +3670,9 @@ struct cxl_region *cxl_create_region(struct cxl_root_decoder *cxlrd,
>  		return ERR_PTR(-ENODEV);
>  	}
>  
> +	if (no_dax)
> +		set_bit(CXL_REGION_F_NO_DAX, &cxlr->flags);
> +
>  	return cxlr;
>  }
>  EXPORT_SYMBOL_NS_GPL(cxl_create_region, "CXL");
> @@ -3831,6 +3836,9 @@ static int cxl_region_probe(struct device *dev)
>  	if (rc)
>  		return rc;
>  
> +	if (test_bit(CXL_REGION_F_NO_DAX, &cxlr->flags))
> +		return 0;
> +
>  	switch (cxlr->mode) {
>  	case CXL_PARTMODE_PMEM:
>  		return devm_cxl_add_pmem_region(cxlr);
> diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> index c35620c24c8f..2eb927c9229c 100644
> --- a/drivers/cxl/cxl.h
> +++ b/drivers/cxl/cxl.h
> @@ -405,6 +405,9 @@ struct cxl_region_params {
>   */
>  #define CXL_REGION_F_NEEDS_RESET 1
>  
> +/* Allow Type2 drivers to specify if a dax region should not be created. */
> +#define CXL_REGION_F_NO_DAX 2
> +
>  /**
>   * struct cxl_region - CXL region
>   * @dev: This region's device
> diff --git a/include/cxl/cxl.h b/include/cxl/cxl.h
> index 133d6db3a70a..2bb495f78239 100644
> --- a/include/cxl/cxl.h
> +++ b/include/cxl/cxl.h
> @@ -262,7 +262,8 @@ struct cxl_endpoint_decoder *cxl_request_dpa(struct cxl_memdev *cxlmd,
>  					     resource_size_t alloc);
>  int cxl_dpa_free(struct cxl_endpoint_decoder *cxled);
>  struct cxl_region *cxl_create_region(struct cxl_root_decoder *cxlrd,
> -				     struct cxl_endpoint_decoder *cxled, int ways);
> +				     struct cxl_endpoint_decoder *cxled, int ways,
> +				     bool no_dax);
>  
>  int cxl_accel_region_detach(struct cxl_endpoint_decoder *cxled);
>  #endif