[PATCH v3 13/18] cxl/region: Add function to find a port's switch decoder by range

Robert Richter
2025-02-11T09:55:09Z

Factor out code to find the switch decoder of a port for a specific
address range. Reuse the code to search a root decoder, create the
function cxl_port_find_switch_decoder() and rework
match_root_decoder_by_range() to be usable for switch decoders too.

Signed-off-by: Robert Richter <rrichter@amd.com>
Reviewed-by: Gregory Price <gourry@gourry.net>
Tested-by: Gregory Price <gourry@gourry.net>
---
drivers/cxl/core/region.c | 48 +++++++++++++++++++++++----------------
1 file changed, 28 insertions(+), 20 deletions(-)

diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
index cfcd235f311e..72e991e7d9ab 100644
--- a/drivers/cxl/core/region.c
+++ b/drivers/cxl/core/region.c
@@ -3189,28 +3189,44 @@ static int devm_cxl_add_dax_region(struct cxl_region *cxlr)
return rc;
}

-static int match_root_decoder_by_range(struct device *dev,
- const void *data)
+static int match_decoder_by_range(struct device *dev, const void *data)
{
const struct range *r1, *r2 = data;
- struct cxl_root_decoder *cxlrd;
+ struct cxl_decoder *cxld;

- if (!is_root_decoder(dev))
+ if (!is_switch_decoder(dev))
return 0;

- cxlrd = to_cxl_root_decoder(dev);
- r1 = &cxlrd->cxlsd.cxld.hpa_range;
+ cxld = to_cxl_decoder(dev);
+ r1 = &cxld->hpa_range;
return range_contains(r1, r2);
}

+static struct cxl_decoder *
+cxl_port_find_switch_decoder(struct cxl_port *port, struct range *hpa)
+{
+ /*
+ * device_find_child() increments the reference count of the
+ * the switch decoder's parent port to protect the reference
+ * to its child. The port is already a parent of the endpoint
+ * decoder's port, at least indirectly in the port hierarchy.
+ * Thus, the endpoint already holds a reference for the parent
+ * port of the switch decoder. Free the unnecessary reference
+ * here.
+ */
+ struct device *cxld_dev __free(put_device) =
+ device_find_child(&port->dev, hpa, match_decoder_by_range);
+
+ return cxld_dev ? to_cxl_decoder(cxld_dev) : NULL;
+}
+
static struct cxl_root_decoder *
cxl_find_root_decoder(struct cxl_endpoint_decoder *cxled)
{
struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
struct cxl_port *iter = cxled_to_port(cxled);
- struct cxl_decoder *cxld = &cxled->cxld;
+ struct cxl_decoder *root, *cxld = &cxled->cxld;
struct range *hpa = &cxld->hpa_range;
- struct device *cxlrd_dev;

while (iter && !is_cxl_root(iter))
iter = to_cxl_port(iter->dev.parent);
@@ -3218,9 +3234,8 @@ cxl_find_root_decoder(struct cxl_endpoint_decoder *cxled)
if (!iter)
return NULL;

- cxlrd_dev = device_find_child(&iter->dev, hpa,
- match_root_decoder_by_range);
- if (!cxlrd_dev) {
+ root = cxl_port_find_switch_decoder(iter, hpa);
+ if (!root) {
dev_err(cxlmd->dev.parent,
"%s:%s no CXL window for range %#llx:%#llx\n",
dev_name(&cxlmd->dev), dev_name(&cxld->dev),
@@ -3228,16 +3243,9 @@ cxl_find_root_decoder(struct cxl_endpoint_decoder *cxled)
return NULL;
}

- /*
- * device_find_child() created a reference to the root
- * decoder. Since the root decoder exists as long as the root
- * port exists and the endpoint already holds a reference to
- * the root port, this additional reference is not needed.
- * Free it here.
- */
- put_device(cxlrd_dev);

- return to_cxl_root_decoder(cxlrd_dev);
+
+ return to_cxl_root_decoder(&root->dev);
}

static int match_region_by_range(struct device *dev, const void *data)
--
2.39.5