Re: [PATCH v12 18/23] cxl: allow region creation by type2 drivers

[Dave Jiang <dave.jiang@intel.com>]

On 3/31/25 7:45 AM, alejandro.lucero-palau@amd.com wrote:
> From: Alejandro Lucero <alucerop@amd.com>
> 
> Creating a CXL region requires userspace intervention through the cxl
> sysfs files. Type2 support should allow accelerator drivers to create
> such cxl region from kernel code.
> 
> Adding that functionality and integrating it with current support for
> memory expanders.
> 
> Based on https://lore.kernel.org/linux-cxl/168592159835.1948938.1647215579839222774.stgit@dwillia2-xfh.jf.intel.com/
> 
> Signed-off-by: Alejandro Lucero <alucerop@amd.com>
> ---
>  drivers/cxl/core/region.c | 135 +++++++++++++++++++++++++++++++++++---
>  drivers/cxl/port.c        |   5 +-
>  include/cxl/cxl.h         |   4 ++
>  3 files changed, 135 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index 892fb799bf46..f2e1d5719a70 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -2310,6 +2310,17 @@ static int cxl_region_detach(struct cxl_endpoint_decoder *cxled)
>  	return rc;
>  }
>  
> +int cxl_accel_region_detach(struct cxl_endpoint_decoder *cxled)
> +{
> +	int rc;
> +
> +	guard(rwsem_write)(&cxl_region_rwsem);
> +	cxled->part = -1;
> +	rc = cxl_region_detach(cxled);
> +	return rc;
> +}
> +EXPORT_SYMBOL_NS_GPL(cxl_accel_region_detach, "CXL");
> +
>  void cxl_decoder_kill_region(struct cxl_endpoint_decoder *cxled)
>  {
>  	down_write(&cxl_region_rwsem);
> @@ -2816,6 +2827,14 @@ cxl_find_region_by_name(struct cxl_root_decoder *cxlrd, const char *name)
>  	return to_cxl_region(region_dev);
>  }
>  
> +static void drop_region(struct cxl_region *cxlr)
> +{
> +	struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(cxlr->dev.parent);
> +	struct cxl_port *port = cxlrd_to_port(cxlrd);
> +
> +	devm_release_action(port->uport_dev, unregister_region, cxlr);
> +}
> +
>  static ssize_t delete_region_store(struct device *dev,
>  				   struct device_attribute *attr,
>  				   const char *buf, size_t len)
> @@ -3520,14 +3539,12 @@ static int __construct_region(struct cxl_region *cxlr,
>  	return 0;
>  }
>  
> -/* Establish an empty region covering the given HPA range */
> -static struct cxl_region *construct_region(struct cxl_root_decoder *cxlrd,
> -					   struct cxl_endpoint_decoder *cxled)
> +static struct cxl_region *construct_region_begin(struct cxl_root_decoder *cxlrd,
> +						 struct cxl_endpoint_decoder *cxled)
>  {
>  	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
> -	struct cxl_port *port = cxlrd_to_port(cxlrd);
>  	struct cxl_dev_state *cxlds = cxlmd->cxlds;
> -	int rc, part = READ_ONCE(cxled->part);
> +	int part = READ_ONCE(cxled->part);
>  	struct cxl_region *cxlr;
>  
>  	do {
> @@ -3536,13 +3553,23 @@ static struct cxl_region *construct_region(struct cxl_root_decoder *cxlrd,
>  				       cxled->cxld.target_type);
>  	} while (IS_ERR(cxlr) && PTR_ERR(cxlr) == -EBUSY);
>  
> -	if (IS_ERR(cxlr)) {
> +	if (IS_ERR(cxlr))
>  		dev_err(cxlmd->dev.parent,
>  			"%s:%s: %s failed assign region: %ld\n",
>  			dev_name(&cxlmd->dev), dev_name(&cxled->cxld.dev),
>  			__func__, PTR_ERR(cxlr));
> -		return cxlr;
> -	}
> +	return cxlr;
> +}
> +
> +/* Establish an empty region covering the given HPA range */
> +static struct cxl_region *construct_region(struct cxl_root_decoder *cxlrd,
> +					   struct cxl_endpoint_decoder *cxled)
> +{
> +	struct cxl_port *port = cxlrd_to_port(cxlrd);
> +	struct cxl_region *cxlr;
> +	int rc;
> +
> +	cxlr = construct_region_begin(cxlrd, cxled);
>  
>  	rc = __construct_region(cxlr, cxlrd, cxled);
>  	if (rc) {
> @@ -3553,6 +3580,98 @@ static struct cxl_region *construct_region(struct cxl_root_decoder *cxlrd,
>  	return cxlr;
>  }
>  
> +static struct cxl_region *
> +__construct_new_region(struct cxl_root_decoder *cxlrd,
> +		       struct cxl_endpoint_decoder *cxled, int ways)
> +{
> +	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
> +	struct cxl_decoder *cxld = &cxlrd->cxlsd.cxld;
> +	struct cxl_region_params *p;
> +	struct cxl_region *cxlr;
> +	int rc;
> +
> +	cxlr = construct_region_begin(cxlrd, cxled);
> +	if (IS_ERR(cxlr))
> +		return cxlr;
> +
> +	guard(rwsem_write)(&cxl_region_rwsem);
> +
> +	/*
> +	 * Sanity check. This should not happen with an accel driver handling
> +	 * the region creation.
> +	 */
> +	p = &cxlr->params;
> +	if (p->state >= CXL_CONFIG_INTERLEAVE_ACTIVE) {
> +		dev_err(cxlmd->dev.parent,
> +			"%s:%s: %s  unexpected region state\n",
> +			dev_name(&cxlmd->dev), dev_name(&cxled->cxld.dev),
> +			__func__);
> +		rc = -EBUSY;
> +		goto err;
> +	}
> +
> +	rc = set_interleave_ways(cxlr, ways);
> +	if (rc)
> +		goto err;
> +
> +	rc = set_interleave_granularity(cxlr, cxld->interleave_granularity);
> +	if (rc)
> +		goto err;
> +
> +	rc = alloc_hpa(cxlr, resource_size(cxled->dpa_res));
> +	if (rc)
> +		goto err;
> +
> +	down_read(&cxl_dpa_rwsem);
> +	rc = cxl_region_attach(cxlr, cxled, 0);> +	up_read(&cxl_dpa_rwsem);
> +> +	if (rc)
> +		goto err;

	scoped_guard(rwsem_read, &cxl_dpa_rwsem) {
		rc = cxl_region_attach(cxlr, cxled, 0);
		if (rc)
			goto err;
	}



> +
> +	rc = cxl_region_decode_commit(cxlr);
> +	if (rc)
> +		goto err;
> +
> +	p->state = CXL_CONFIG_COMMIT;
> +
> +	return cxlr;
> +err:
> +	drop_region(cxlr);
> +	return ERR_PTR(rc);
> +}
> +
> +/**
> + * cxl_create_region - Establish a region given an endpoint decoder
> + * @cxlrd: root decoder to allocate HPA
> + * @cxled: endpoint decoder with reserved DPA capacity
> + * @ways: interleave ways required
> + *
> + * 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_region *cxlr;
> +
> +	mutex_lock(&cxlrd->range_lock);
> +	cxlr = __construct_new_region(cxlrd, cxled, ways);> +	mutex_unlock(&cxlrd->range_lock);
> +
> +	if (IS_ERR(cxlr))
> +		return cxlr;
	scoped_guard(mutex, &cxlrd->range_lock) {
		cxlr = __construct_new_region(cxlrd, cxled, ways);
		if (IS_ERR(cxlr))
			return cxlr;
	}

DJ

> +
> +	if (device_attach(&cxlr->dev) <= 0) {
> +		dev_err(&cxlr->dev, "failed to create region\n");
> +		drop_region(cxlr);
> +		return ERR_PTR(-ENODEV);
> +	}
> +
> +	return cxlr;
> +}
> +EXPORT_SYMBOL_NS_GPL(cxl_create_region, "CXL");
> +
>  int cxl_add_to_region(struct cxl_port *root, struct cxl_endpoint_decoder *cxled)
>  {
>  	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
> diff --git a/drivers/cxl/port.c b/drivers/cxl/port.c
> index d2bfd1ff5492..f352f2b1c481 100644
> --- a/drivers/cxl/port.c
> +++ b/drivers/cxl/port.c
> @@ -33,6 +33,7 @@ static void schedule_detach(void *cxlmd)
>  static int discover_region(struct device *dev, void *root)
>  {
>  	struct cxl_endpoint_decoder *cxled;
> +	struct cxl_memdev *cxlmd;
>  	int rc;
>  
>  	if (!is_endpoint_decoder(dev))
> @@ -42,7 +43,9 @@ static int discover_region(struct device *dev, void *root)
>  	if ((cxled->cxld.flags & CXL_DECODER_F_ENABLE) == 0)
>  		return 0;
>  
> -	if (cxled->state != CXL_DECODER_STATE_AUTO)
> +	cxlmd = cxled_to_memdev(cxled);
> +	if (cxled->state != CXL_DECODER_STATE_AUTO ||
> +	    cxlmd->cxlds->type == CXL_DEVTYPE_DEVMEM)
>  		return 0;
>  
>  	/*
> diff --git a/include/cxl/cxl.h b/include/cxl/cxl.h
> index 22061646b147..133d6db3a70a 100644
> --- a/include/cxl/cxl.h
> +++ b/include/cxl/cxl.h
> @@ -261,4 +261,8 @@ 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);
> +struct cxl_region *cxl_create_region(struct cxl_root_decoder *cxlrd,
> +				     struct cxl_endpoint_decoder *cxled, int ways);
> +
> +int cxl_accel_region_detach(struct cxl_endpoint_decoder *cxled);
>  #endif