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

[Alejandro Lucero Palau <alucerop@amd.com>]

On 7/16/24 06:52, Li, Ming4 wrote:
> On 7/16/2024 1:28 AM, 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");
>> +		return;
>> +	}
>> +
>> +	cxl->endpoint = cxl_acquire_endpoint(cxl->cxlmd);
>> +	if (IS_ERR(cxl->endpoint))
>> +		pci_info(pci_dev, "CXL accel acquire endpoint failed");
>> +
>> +	cxl_release_endpoint(cxl->cxlmd, cxl->endpoint);
> there is no need to invoke cxl_release_endpoint() if cxl_acquire_endpoint() failed. right?
>
>

Right. BTW,  I do that in a following patch.

I should just add the functions to the CXL core here, and to use them in 
a subsequent patch where it makes sense.

Thanks


>>   }
>>   
>>   
>> 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
>