Re: [PATCH v6 4/9] dax/cxl, hmem: Initialize hmem early and defer dax_cxl binding

Dave Jiang
2026-02-18T15:54:54Z

On 2/9/26 11:44 PM, Smita Koralahalli wrote:
> From: Dan Williams <dan.j.williams@intel.com>
>
> Move hmem/ earlier in the dax Makefile so that hmem_init() runs before
> dax_cxl.
>
> In addition, defer registration of the dax_cxl driver to a workqueue
> instead of using module_cxl_driver(). This ensures that dax_hmem has
> an opportunity to initialize and register its deferred callback and make
> ownership decisions before dax_cxl begins probing and claiming Soft
> Reserved ranges.
>
> Mark the dax_cxl driver as PROBE_PREFER_ASYNCHRONOUS so its probe runs
> out of line from other synchronous probing avoiding ordering
> dependencies while coordinating ownership decisions with dax_hmem.
>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@amd.com>

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

> ---
> drivers/dax/Makefile | 3 +--
> drivers/dax/cxl.c | 27 ++++++++++++++++++++++++++-
> 2 files changed, 27 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/dax/Makefile b/drivers/dax/Makefile
> index 5ed5c39857c8..70e996bf1526 100644
> --- a/drivers/dax/Makefile
> +++ b/drivers/dax/Makefile
> @@ -1,4 +1,5 @@
> # SPDX-License-Identifier: GPL-2.0
> +obj-y += hmem/
> obj-$(CONFIG_DAX) += dax.o
> obj-$(CONFIG_DEV_DAX) += device_dax.o
> obj-$(CONFIG_DEV_DAX_KMEM) += kmem.o
> @@ -10,5 +11,3 @@ dax-y += bus.o
> device_dax-y := device.o
> dax_pmem-y := pmem.o
> dax_cxl-y := cxl.o
> -
> -obj-y += hmem/
> diff --git a/drivers/dax/cxl.c b/drivers/dax/cxl.c
> index 13cd94d32ff7..a2136adfa186 100644
> --- a/drivers/dax/cxl.c
> +++ b/drivers/dax/cxl.c
> @@ -38,10 +38,35 @@ static struct cxl_driver cxl_dax_region_driver = {
> .id = CXL_DEVICE_DAX_REGION,
> .drv = {
> .suppress_bind_attrs = true,
> + .probe_type = PROBE_PREFER_ASYNCHRONOUS,
> },
> };
>
> -module_cxl_driver(cxl_dax_region_driver);
> +static void cxl_dax_region_driver_register(struct work_struct *work)
> +{
> + cxl_driver_register(&cxl_dax_region_driver);
> +}
> +
> +static DECLARE_WORK(cxl_dax_region_driver_work, cxl_dax_region_driver_register);
> +
> +static int __init cxl_dax_region_init(void)
> +{
> + /*
> + * Need to resolve a race with dax_hmem wanting to drive regions
> + * instead of CXL
> + */
> + queue_work(system_long_wq, &cxl_dax_region_driver_work);
> + return 0;
> +}
> +module_init(cxl_dax_region_init);
> +
> +static void __exit cxl_dax_region_exit(void)
> +{
> + flush_work(&cxl_dax_region_driver_work);
> + cxl_driver_unregister(&cxl_dax_region_driver);
> +}
> +module_exit(cxl_dax_region_exit);
> +
> MODULE_ALIAS_CXL(CXL_DEVICE_DAX_REGION);
> MODULE_DESCRIPTION("CXL DAX: direct access to CXL regions");
> MODULE_LICENSE("GPL");