Re: [PATCH 2/6] cxl/mem: Arrange for always-synchronous memdev attach

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

On 12/3/25 7:21 PM, Dan Williams wrote:
> In preparation for CXL accelerator drivers that have a hard dependency on
> CXL capability initialization, arrange for cxl_mem_probe() to always run
> synchronous with the device_add() of cxl_memdev instances. I.e.
> cxl_mem_driver registration is always complete before the first memdev
> creation event.
> 
> At present, cxl_pci does not care about the attach state of the cxl_memdev
> because all generic memory expansion functionality can be handled by the
> cxl_core. For accelerators, however, that driver needs to perform driver
> specific initialization if CXL is available, or execute a fallback to PCIe
> only operation.
> 
> This synchronous attach guarantee is also needed for Soft Reserve Recovery,
> which is an effort that needs to assert that devices have had a chance to
> attach before making a go / no-go decision on proceeding with CXL subsystem
> initialization.
> 
> By moving devm_cxl_add_memdev() to cxl_mem.ko it removes async module
> loading as one reason that a memdev may not be attached upon return from
> devm_cxl_add_memdev().
> 
> Cc: Smita Koralahalli <Smita.KoralahalliChannabasappa@amd.com>
> Cc: Alejandro Lucero <alucerop@amd.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Reviewed-by: Dave Jiang <dave.jiang@intel.com>

> ---
>  drivers/cxl/Kconfig       |  2 +-
>  drivers/cxl/cxlmem.h      |  2 ++
>  drivers/cxl/core/memdev.c | 10 +++++++---
>  drivers/cxl/mem.c         | 17 +++++++++++++++++
>  4 files changed, 27 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/cxl/Kconfig b/drivers/cxl/Kconfig
> index 48b7314afdb8..f1361ed6a0d4 100644
> --- a/drivers/cxl/Kconfig
> +++ b/drivers/cxl/Kconfig
> @@ -22,6 +22,7 @@ if CXL_BUS
>  config CXL_PCI
>  	tristate "PCI manageability"
>  	default CXL_BUS
> +	select CXL_MEM
>  	help
>  	  The CXL specification defines a "CXL memory device" sub-class in the
>  	  PCI "memory controller" base class of devices. Device's identified by
> @@ -89,7 +90,6 @@ config CXL_PMEM
>  
>  config CXL_MEM
>  	tristate "CXL: Memory Expansion"
> -	depends on CXL_PCI
>  	default CXL_BUS
>  	help
>  	  The CXL.mem protocol allows a device to act as a provider of "System
> diff --git a/drivers/cxl/cxlmem.h b/drivers/cxl/cxlmem.h
> index c12ab4fc9512..012e68acad34 100644
> --- a/drivers/cxl/cxlmem.h
> +++ b/drivers/cxl/cxlmem.h
> @@ -95,6 +95,8 @@ static inline bool is_cxl_endpoint(struct cxl_port *port)
>  	return is_cxl_memdev(port->uport_dev);
>  }
>  
> +struct cxl_memdev *__devm_cxl_add_memdev(struct device *host,
> +					 struct cxl_dev_state *cxlds);
>  struct cxl_memdev *devm_cxl_add_memdev(struct device *host,
>  				       struct cxl_dev_state *cxlds);
>  int devm_cxl_sanitize_setup_notifier(struct device *host,
> diff --git a/drivers/cxl/core/memdev.c b/drivers/cxl/core/memdev.c
> index 4dff7f44d908..7a4153e1c6a7 100644
> --- a/drivers/cxl/core/memdev.c
> +++ b/drivers/cxl/core/memdev.c
> @@ -1050,8 +1050,12 @@ static const struct file_operations cxl_memdev_fops = {
>  	.llseek = noop_llseek,
>  };
>  
> -struct cxl_memdev *devm_cxl_add_memdev(struct device *host,
> -				       struct cxl_dev_state *cxlds)
> +/*
> + * Core helper for devm_cxl_add_memdev() that wants to both create a device and
> + * assert to the caller that upon return cxl_mem::probe() has been invoked.
> + */
> +struct cxl_memdev *__devm_cxl_add_memdev(struct device *host,
> +					 struct cxl_dev_state *cxlds)
>  {
>  	struct cxl_memdev *cxlmd;
>  	struct device *dev;
> @@ -1093,7 +1097,7 @@ struct cxl_memdev *devm_cxl_add_memdev(struct device *host,
>  	put_device(dev);
>  	return ERR_PTR(rc);
>  }
> -EXPORT_SYMBOL_NS_GPL(devm_cxl_add_memdev, "CXL");
> +EXPORT_SYMBOL_FOR_MODULES(__devm_cxl_add_memdev, "cxl_mem");
>  
>  static void sanitize_teardown_notifier(void *data)
>  {
> diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c
> index 6e6777b7bafb..55883797ab2d 100644
> --- a/drivers/cxl/mem.c
> +++ b/drivers/cxl/mem.c
> @@ -201,6 +201,22 @@ static int cxl_mem_probe(struct device *dev)
>  	return devm_add_action_or_reset(dev, enable_suspend, NULL);
>  }
>  
> +/**
> + * devm_cxl_add_memdev - Add a CXL memory device
> + * @host: devres alloc/release context and parent for the memdev
> + * @cxlds: CXL device state to associate with the memdev
> + *
> + * Upon return the device will have had a chance to attach to the
> + * cxl_mem driver, but may fail if the CXL topology is not ready
> + * (hardware CXL link down, or software platform CXL root not attached)
> + */
> +struct cxl_memdev *devm_cxl_add_memdev(struct device *host,
> +				       struct cxl_dev_state *cxlds)
> +{
> +	return __devm_cxl_add_memdev(host, cxlds);
> +}
> +EXPORT_SYMBOL_NS_GPL(devm_cxl_add_memdev, "CXL");
> +
>  static ssize_t trigger_poison_list_store(struct device *dev,
>  					 struct device_attribute *attr,
>  					 const char *buf, size_t len)
> @@ -248,6 +264,7 @@ static struct cxl_driver cxl_mem_driver = {
>  	.probe = cxl_mem_probe,
>  	.id = CXL_DEVICE_MEMORY_EXPANDER,
>  	.drv = {
> +		.probe_type = PROBE_FORCE_SYNCHRONOUS,
>  		.dev_groups = cxl_mem_groups,
>  	},
>  };