Re: [PATCH v8 23/27] cxl: add region flag for precluding a device memory to be used for dax

[Jonathan Cameron <Jonathan.Cameron@huawei.com>]

On Mon, 16 Dec 2024 16:10:38 +0000
<alejandro.lucero-palau@amd.com> wrote:

> From: Alejandro Lucero <alucerop@amd.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.

So this is presented as something a type 2 driver would chose to set
or not. That feels premature if for now they are all going to set
it? 
> 
> Signed-off-by: Alejandro Lucero <alucerop@amd.com>
> Reviewed-by: Zhi Wang <zhiw@nvidia.com>
> ---
>  drivers/cxl/core/region.c | 11 ++++++++++-
>  drivers/cxl/cxl.h         |  3 +++
>  drivers/cxl/cxlmem.h      |  3 ++-
>  include/cxl/cxl.h         |  3 ++-
>  4 files changed, 17 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index a24d8678e8dc..aeaa6868e556 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -3557,12 +3557,14 @@ __construct_new_region(struct cxl_root_decoder *cxlrd,
>   * cxl_create_region - Establish a region given an endpoint decoder
>   * @cxlrd: root decoder to allocate HPA
>   * @cxled: endpoint decoder with reserved DPA capacity
> + * @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)
> +				     struct cxl_endpoint_decoder *cxled,
> +				     bool no_dax)
>  {
>  	struct cxl_region *cxlr;
>  
> @@ -3578,6 +3580,10 @@ struct cxl_region *cxl_create_region(struct cxl_root_decoder *cxlrd,
>  		drop_region(cxlr);
>  		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");
> @@ -3713,6 +3719,9 @@ 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_DECODER_PMEM:
>  		return devm_cxl_add_pmem_region(cxlr);
> diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> index 57d6dda3fb4a..cc9e3d859fa6 100644
> --- a/drivers/cxl/cxl.h
> +++ b/drivers/cxl/cxl.h
> @@ -521,6 +521,9 @@ 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/drivers/cxl/cxlmem.h b/drivers/cxl/cxlmem.h
> index 9d874f1cb3bf..712f25f494e0 100644
> --- a/drivers/cxl/cxlmem.h
> +++ b/drivers/cxl/cxlmem.h
> @@ -875,5 +875,6 @@ struct seq_file;
>  struct dentry *cxl_debugfs_create_dir(const char *dir);
>  void cxl_dpa_debug(struct seq_file *file, struct cxl_dev_state *cxlds);
>  struct cxl_region *cxl_create_region(struct cxl_root_decoder *cxlrd,
> -				     struct cxl_endpoint_decoder *cxled);
> +				     struct cxl_endpoint_decoder *cxled,
> +				     bool no_dax);
>  #endif /* __CXL_MEM_H__ */
> diff --git a/include/cxl/cxl.h b/include/cxl/cxl.h
> index e0ea5b801a2e..14be26358f9c 100644
> --- a/include/cxl/cxl.h
> +++ b/include/cxl/cxl.h
> @@ -61,7 +61,8 @@ struct cxl_endpoint_decoder *cxl_request_dpa(struct cxl_memdev *cxlmd,
>  					     resource_size_t max);
>  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);
> +				     struct cxl_endpoint_decoder *cxled,
> +				     bool no_dax);
>  
>  int cxl_accel_region_detach(struct cxl_endpoint_decoder *cxled);
>  #endif