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Message-ID: <cb9a5b27-13eb-40ee-9d9b-fb596cdf4caa@intel.com>
Date: Thu, 4 Dec 2025 13:03:27 -0700
From: Dave Jiang <dave.jiang@...el.com>
To: Dan Williams <dan.j.williams@...el.com>
Cc: linux-cxl@...r.kernel.org, linux-kernel@...r.kernel.org,
Smita.KoralahalliChannabasappa@....com, alison.schofield@...el.com,
terry.bowman@....com, alejandro.lucero-palau@....com,
linux-pci@...r.kernel.org, Jonathan.Cameron@...wei.com,
Alejandro Lucero <alucerop@....com>
Subject: Re: [PATCH 6/6] cxl/mem: Introduce a memdev creation ->probe()
operation
On 12/3/25 7:21 PM, Dan Williams wrote:
> Allow for a driver to pass a routine to be called in cxl_mem_probe()
> context. This ability is inspired by and mirrors the semantics of
> faux_device_create(). It allows for the caller to run CXL-topology
> attach-dependent logic on behalf of the caller.
>
> This capability is needed for CXL accelerator device drivers that need to
> make decisions about enabling CXL dependent functionality in the device, or
> falling back to PCIe-only operation.
>
> The probe callback runs after the port topology is successfully attached
> for the given memdev.
>
> Cc: Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
> Cc: Alejandro Lucero <alucerop@....com>
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
Reviewed-by: Dave Jiang <dave.jiang@...el.com>
> ---
> drivers/cxl/cxlmem.h | 12 ++++++++--
> drivers/cxl/core/memdev.c | 46 +++++++++++++++++++++++++++++-------
> drivers/cxl/mem.c | 12 ++++++++--
> drivers/cxl/pci.c | 2 +-
> tools/testing/cxl/test/mem.c | 2 +-
> 5 files changed, 60 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/cxl/cxlmem.h b/drivers/cxl/cxlmem.h
> index 9db31c7993c4..ed759f88b21f 100644
> --- a/drivers/cxl/cxlmem.h
> +++ b/drivers/cxl/cxlmem.h
> @@ -34,6 +34,10 @@
> (FIELD_GET(CXLMDEV_RESET_NEEDED_MASK, status) != \
> CXLMDEV_RESET_NEEDED_NOT)
>
> +struct cxl_memdev_ops {
> + int (*probe)(struct cxl_memdev *cxlmd);
> +};
> +
> /**
> * struct cxl_memdev - CXL bus object representing a Type-3 Memory Device
> * @dev: driver core device object
> @@ -43,6 +47,7 @@
> * @cxl_nvb: coordinate removal of @cxl_nvd if present
> * @cxl_nvd: optional bridge to an nvdimm if the device supports pmem
> * @endpoint: connection to the CXL port topology for this memory device
> + * @ops: incremental caller specific probe routine
> * @id: id number of this memdev instance.
> * @depth: endpoint port depth
> * @scrub_cycle: current scrub cycle set for this device
> @@ -59,6 +64,7 @@ struct cxl_memdev {
> struct cxl_nvdimm_bridge *cxl_nvb;
> struct cxl_nvdimm *cxl_nvd;
> struct cxl_port *endpoint;
> + const struct cxl_memdev_ops *ops;
> int id;
> int depth;
> u8 scrub_cycle;
> @@ -95,8 +101,10 @@ 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 cxl_dev_state *cxlds);
> -struct cxl_memdev *devm_cxl_add_memdev(struct cxl_dev_state *cxlds);
> +struct cxl_memdev *__devm_cxl_add_memdev(struct cxl_dev_state *cxlds,
> + const struct cxl_memdev_ops *ops);
> +struct cxl_memdev *devm_cxl_add_memdev(struct cxl_dev_state *cxlds,
> + const struct cxl_memdev_ops *ops);
> int devm_cxl_sanitize_setup_notifier(struct device *host,
> struct cxl_memdev *cxlmd);
> struct cxl_memdev_state;
> diff --git a/drivers/cxl/core/memdev.c b/drivers/cxl/core/memdev.c
> index 7d85ba25835a..41f1964d8cbf 100644
> --- a/drivers/cxl/core/memdev.c
> +++ b/drivers/cxl/core/memdev.c
> @@ -648,7 +648,8 @@ static void detach_memdev(struct work_struct *work)
> static struct lock_class_key cxl_memdev_key;
>
> static struct cxl_memdev *cxl_memdev_alloc(struct cxl_dev_state *cxlds,
> - const struct file_operations *fops)
> + const struct file_operations *fops,
> + const struct cxl_memdev_ops *ops)
> {
> struct cxl_memdev *cxlmd;
> struct device *dev;
> @@ -664,6 +665,8 @@ static struct cxl_memdev *cxl_memdev_alloc(struct cxl_dev_state *cxlds,
> goto err;
> cxlmd->id = rc;
> cxlmd->depth = -1;
> + cxlmd->ops = ops;
> + cxlmd->endpoint = ERR_PTR(-ENXIO);
>
> dev = &cxlmd->dev;
> device_initialize(dev);
> @@ -1077,17 +1080,48 @@ static int cxlmd_add(struct cxl_memdev *cxlmd, struct cxl_dev_state *cxlds)
> DEFINE_FREE(put_cxlmd, struct cxl_memdev *,
> if (!IS_ERR_OR_NULL(_T)) put_device(&_T->dev);)
>
> +static struct cxl_memdev *cxl_memdev_autoremove(struct cxl_memdev *cxlmd)
> +{
> + struct cxl_memdev *ret = cxlmd;
> + int rc;
> +
> + /*
> + * If ops is provided fail if the driver is not attached upon
> + * return. The ->endpoint ERR_PTR may have a more precise error
> + * code to convey. Note that failure here could be the result of
> + * a race to teardown the CXL port topology. I.e.
> + * cxl_mem_probe() could have succeeded and then cxl_mem unbound
> + * before the lock is acquired.
> + */
> + guard(device)(&cxlmd->dev);
> + if (cxlmd->ops && !cxlmd->dev.driver) {
> + ret = ERR_PTR(-ENXIO);
> + if (IS_ERR(cxlmd->endpoint))
> + ret = ERR_CAST(cxlmd->endpoint);
> + cxl_memdev_unregister(cxlmd);
> + return ret;
> + }
> +
> + rc = devm_add_action_or_reset(cxlmd->cxlds->dev, cxl_memdev_unregister,
> + cxlmd);
> + if (rc)
> + return ERR_PTR(rc);
> +
> + return ret;
> +}
> +
> /*
> * 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 cxl_dev_state *cxlds)
> +struct cxl_memdev *__devm_cxl_add_memdev(struct cxl_dev_state *cxlds,
> + const struct cxl_memdev_ops *ops)
> {
> struct device *dev;
> int rc;
>
> struct cxl_memdev *cxlmd __free(put_cxlmd) =
> - cxl_memdev_alloc(cxlds, &cxl_memdev_fops);
> + cxl_memdev_alloc(cxlds, &cxl_memdev_fops, ops);
> if (IS_ERR(cxlmd))
> return cxlmd;
>
> @@ -1100,11 +1134,7 @@ struct cxl_memdev *__devm_cxl_add_memdev(struct cxl_dev_state *cxlds)
> if (rc)
> return ERR_PTR(rc);
>
> - rc = devm_add_action_or_reset(cxlds->dev, cxl_memdev_unregister,
> - no_free_ptr(cxlmd));
> - if (rc)
> - return ERR_PTR(rc);
> - return cxlmd;
> + return cxl_memdev_autoremove(no_free_ptr(cxlmd));
> }
> EXPORT_SYMBOL_FOR_MODULES(__devm_cxl_add_memdev, "cxl_mem");
>
> diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c
> index 677996c65272..d61f121c6f97 100644
> --- a/drivers/cxl/mem.c
> +++ b/drivers/cxl/mem.c
> @@ -142,6 +142,12 @@ static int cxl_mem_probe(struct device *dev)
> return rc;
> }
>
> + if (cxlmd->ops) {
> + rc = cxlmd->ops->probe(cxlmd);
> + if (rc)
> + return rc;
> + }
> +
> rc = devm_cxl_memdev_edac_register(cxlmd);
> if (rc)
> dev_dbg(dev, "CXL memdev EDAC registration failed rc=%d\n", rc);
> @@ -166,6 +172,7 @@ static int cxl_mem_probe(struct device *dev)
> /**
> * devm_cxl_add_memdev - Add a CXL memory device
> * @cxlds: CXL device state to associate with the memdev
> + * @ops: optional operations to run in cxl_mem::{probe,remove}() context
> *
> * 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
> @@ -174,9 +181,10 @@ static int cxl_mem_probe(struct device *dev)
> * The parent of the resulting device and the devm context for allocations is
> * @cxlds->dev.
> */
> -struct cxl_memdev *devm_cxl_add_memdev(struct cxl_dev_state *cxlds)
> +struct cxl_memdev *devm_cxl_add_memdev(struct cxl_dev_state *cxlds,
> + const struct cxl_memdev_ops *ops)
> {
> - return __devm_cxl_add_memdev(cxlds);
> + return __devm_cxl_add_memdev(cxlds, ops);
> }
> EXPORT_SYMBOL_NS_GPL(devm_cxl_add_memdev, "CXL");
>
> diff --git a/drivers/cxl/pci.c b/drivers/cxl/pci.c
> index 1c6fc5334806..549368a9c868 100644
> --- a/drivers/cxl/pci.c
> +++ b/drivers/cxl/pci.c
> @@ -1006,7 +1006,7 @@ static int cxl_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
> if (rc)
> dev_dbg(&pdev->dev, "No CXL Features discovered\n");
>
> - cxlmd = devm_cxl_add_memdev(cxlds);
> + cxlmd = devm_cxl_add_memdev(cxlds, NULL);
> if (IS_ERR(cxlmd))
> return PTR_ERR(cxlmd);
>
> diff --git a/tools/testing/cxl/test/mem.c b/tools/testing/cxl/test/mem.c
> index 8a22b7601627..cb87e8c0e63c 100644
> --- a/tools/testing/cxl/test/mem.c
> +++ b/tools/testing/cxl/test/mem.c
> @@ -1767,7 +1767,7 @@ static int cxl_mock_mem_probe(struct platform_device *pdev)
>
> cxl_mock_add_event_logs(&mdata->mes);
>
> - cxlmd = devm_cxl_add_memdev(cxlds);
> + cxlmd = devm_cxl_add_memdev(cxlds, NULL);
> if (IS_ERR(cxlmd))
> return PTR_ERR(cxlmd);
>
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