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

alejandro.lucero-palau
2024-07-15T17:28:59Z

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);
}

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