Re: [PATCH v2 08/15] cxl: indicate probe deferral

[Fan Ni <nifan.cxl@gmail.com>]

On Mon, Jul 15, 2024 at 06:28:28PM +0100, alejandro.lucero-palau@amd.com wrote:
> From: Alejandro Lucero <alucerop@amd.com>
> 
> The first stop for a CXL accelerator driver that wants to establish new
> CXL.mem regions is to register a 'struct cxl_memdev. That kicks off
> cxl_mem_probe() to enumerate all 'struct cxl_port' instances in the
> topology up to the root.
> 
> If the root driver has not attached yet the expectation is that the
> driver waits until that link is established. The common cxl_pci_driver
> has reason to keep the 'struct cxl_memdev' device attached to the bus
> until the root driver attaches. An accelerator may want to instead defer
> probing until CXL resources can be acquired.
> 
> Use the @endpoint attribute of a 'struct cxl_memdev' to convey when
> accelerator driver probing should be defferred vs failed. Provide that
> indication via a new cxl_acquire_endpoint() API that can retrieve the
> probe status of the memdev.
> 
> The first consumer of this API is a test driver that excercises the CXL
> Type-2 flow.
> 
> Based on https://lore.kernel.org/linux-cxl/168592149709.1948938.8663425987110396027.stgit@dwillia2-xfh.jf.intel.com/T/#m18497367d2ae38f88e94c06369eaa83fa23e92b2
> 
> Signed-off-by: Alejandro Lucero <alucerop@amd.com>
> Co-developed-by: Dan Williams <dan.j.williams@intel.com>
> ---
>  drivers/cxl/core/memdev.c          | 41 ++++++++++++++++++++++++++++++
>  drivers/cxl/core/port.c            |  2 +-
>  drivers/cxl/mem.c                  |  7 +++--
>  drivers/net/ethernet/sfc/efx_cxl.c | 10 +++++++-
>  include/linux/cxl_accel_mem.h      |  3 +++
>  5 files changed, 59 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/cxl/core/memdev.c b/drivers/cxl/core/memdev.c
> index b902948b121f..d51c8bfb32e3 100644
> --- a/drivers/cxl/core/memdev.c
> +++ b/drivers/cxl/core/memdev.c
> @@ -1137,6 +1137,47 @@ struct cxl_memdev *devm_cxl_add_memdev(struct device *host,
>  }
>  EXPORT_SYMBOL_NS_GPL(devm_cxl_add_memdev, CXL);
>  
> +/*
> + * Try to get a locked reference on a memdev's CXL port topology
> + * connection. Be careful to observe when cxl_mem_probe() has deposited
> + * a probe deferral awaiting the arrival of the CXL root driver
> +*/
> +struct cxl_port *cxl_acquire_endpoint(struct cxl_memdev *cxlmd)
> +{
> +	struct cxl_port *endpoint;
> +	int rc = -ENXIO;
> +
> +	device_lock(&cxlmd->dev);
> +	endpoint = cxlmd->endpoint;
> +	if (!endpoint)
> +		goto err;
> +
> +	if (IS_ERR(endpoint)) {
> +		rc = PTR_ERR(endpoint);
> +		goto err;
> +	}
> +
> +	device_lock(&endpoint->dev);
> +	if (!endpoint->dev.driver)
> +		goto err_endpoint;
> +
> +	return endpoint;
> +
> +err_endpoint:
> +	device_unlock(&endpoint->dev);
> +err:
> +	device_unlock(&cxlmd->dev);
> +	return ERR_PTR(rc);
> +}
> +EXPORT_SYMBOL_NS(cxl_acquire_endpoint, CXL);
> +
> +void cxl_release_endpoint(struct cxl_memdev *cxlmd, struct cxl_port *endpoint)
> +{
> +	device_unlock(&endpoint->dev);
> +	device_unlock(&cxlmd->dev);
> +}
> +EXPORT_SYMBOL_NS(cxl_release_endpoint, CXL);
> +
>  static void sanitize_teardown_notifier(void *data)
>  {
>  	struct cxl_memdev_state *mds = data;
> diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
> index d66c6349ed2d..3c6b896c5f65 100644
> --- a/drivers/cxl/core/port.c
> +++ b/drivers/cxl/core/port.c
> @@ -1553,7 +1553,7 @@ static int add_port_attach_ep(struct cxl_memdev *cxlmd,
>  		 */
>  		dev_dbg(&cxlmd->dev, "%s is a root dport\n",
>  			dev_name(dport_dev));
> -		return -ENXIO;
> +		return -EPROBE_DEFER;
>  	}
>  
>  	parent_port = find_cxl_port(dparent, &parent_dport);
> diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c
> index f76af75a87b7..383a6f4829d3 100644
> --- a/drivers/cxl/mem.c
> +++ b/drivers/cxl/mem.c
> @@ -145,13 +145,16 @@ static int cxl_mem_probe(struct device *dev)
>  		return rc;
>  
>  	rc = devm_cxl_enumerate_ports(cxlmd);
> -	if (rc)
> +	if (rc) {
> +		cxlmd->endpoint = ERR_PTR(rc);
>  		return rc;
> +	}
>  
>  	parent_port = cxl_mem_find_port(cxlmd, &dport);
>  	if (!parent_port) {
>  		dev_err(dev, "CXL port topology not found\n");
> -		return -ENXIO;
> +		cxlmd->endpoint = ERR_PTR(-EPROBE_DEFER);
> +		return -EPROBE_DEFER;
>  	}
>  
>  	if (resource_size(&cxlds->pmem_res) && IS_ENABLED(CONFIG_CXL_PMEM)) {
> diff --git a/drivers/net/ethernet/sfc/efx_cxl.c b/drivers/net/ethernet/sfc/efx_cxl.c
> index 0abe66490ef5..2cf4837ddfc1 100644
> --- a/drivers/net/ethernet/sfc/efx_cxl.c
> +++ b/drivers/net/ethernet/sfc/efx_cxl.c
> @@ -65,8 +65,16 @@ void efx_cxl_init(struct efx_nic *efx)
>  	}
>  
>  	cxl->cxlmd = devm_cxl_add_memdev(&pci_dev->dev, cxl->cxlds);
> -	if (IS_ERR(cxl->cxlmd))
> +	if (IS_ERR(cxl->cxlmd)) {
>  		pci_info(pci_dev, "CXL accel memdev creation failed");
pci_err()?
> +		return;
> +	}
> +
> +	cxl->endpoint = cxl_acquire_endpoint(cxl->cxlmd);
> +	if (IS_ERR(cxl->endpoint))
> +		pci_info(pci_dev, "CXL accel acquire endpoint failed");
pci_err()?
> +
> +	cxl_release_endpoint(cxl->cxlmd, cxl->endpoint);
>  }
>  
>  
> diff --git a/include/linux/cxl_accel_mem.h b/include/linux/cxl_accel_mem.h
> index 442ed9862292..701910021df8 100644
> --- a/include/linux/cxl_accel_mem.h
> +++ b/include/linux/cxl_accel_mem.h
> @@ -29,4 +29,7 @@ int cxl_await_media_ready(struct cxl_dev_state *cxlds);
>  
>  struct cxl_memdev *devm_cxl_add_memdev(struct device *host,
>  				       struct cxl_dev_state *cxlds);
> +
> +struct cxl_port *cxl_acquire_endpoint(struct cxl_memdev *cxlmd);
> +void cxl_release_endpoint(struct cxl_memdev *cxlmd, struct cxl_port *endpoint);
>  #endif
> -- 
> 2.17.1
>