[v12,13/23] cxl: define a driver interface for DPA allocation

Commit Message

Lucero Palau, Alejandro March 31, 2025, 2:45 p.m. UTC

From: Alejandro Lucero <[e-mail]>

Region creation involves finding available DPA (device-physical-address)
capacity to map into HPA (host-physical-address) space. Define an API,
cxl_request_dpa(), that tries to allocate the DPA memory the driver
requires to operate. The memory requested should not be bigger than the
max available HPA obtained previously with cxl_get_hpa_freespace.

Based on https://lore.kernel.org/linux-cxl/[e-mail]/

Signed-off-by: Alejandro Lucero <[e-mail]>
Reviewed-by: Ben Cheatham <[e-mail]>
---
 drivers/cxl/core/hdm.c | 83 ++++++++++++++++++++++++++++++++++++++++++
 include/cxl/cxl.h      |  5 +++
 2 files changed, 88 insertions(+)

Patch

diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
index 70cae4ebf8a4..db6d99e07d45 100644
--- a/drivers/cxl/core/hdm.c
+++ b/drivers/cxl/core/hdm.c
@@ -3,6 +3,7 @@ 
 #include <linux/seq_file.h>
 #include <linux/device.h>
 #include <linux/delay.h>
+#include <cxl/cxl.h>
 
 #include "cxlmem.h"
 #include "core.h"
@@ -572,6 +573,7 @@  int cxl_dpa_free(struct cxl_endpoint_decoder *cxled)
 	devm_cxl_dpa_release(cxled);
 	return 0;
 }
+EXPORT_SYMBOL_NS_GPL(cxl_dpa_free, "CXL");
 
 int cxl_dpa_set_part(struct cxl_endpoint_decoder *cxled,
 		     enum cxl_partition_mode mode)
@@ -686,6 +688,87 @@  int cxl_dpa_alloc(struct cxl_endpoint_decoder *cxled, unsigned long long size)
 	return devm_add_action_or_reset(&port->dev, cxl_dpa_release, cxled);
 }
 
+static int find_free_decoder(struct device *dev, const void *data)
+{
+	struct cxl_endpoint_decoder *cxled;
+	struct cxl_port *port;
+
+	if (!is_endpoint_decoder(dev))
+		return 0;
+
+	cxled = to_cxl_endpoint_decoder(dev);
+	port = cxled_to_port(cxled);
+
+	if (cxled->cxld.id != port->hdm_end + 1)
+		return 0;
+
+	return 1;
+}
+
+/**
+ * cxl_request_dpa - search and reserve DPA given input constraints
+ * @cxlmd: memdev with an endpoint port with available decoders
+ * @is_ram: DPA operation mode (ram vs pmem)
+ * @alloc: dpa size required
+ *
+ * Given that a region needs to allocate from limited HPA capacity it
+ * may be the case that a device has more mappable DPA capacity than
+ * available HPA. The expectation is that @alloc is a driver known
+ * value based on the device capacity but it could not be available
+ * due to HPA constraints.
+ *
+ * Returns a pinned cxl_decoder with at least @alloc bytes of capacity
+ * reserved, or an error pointer. The caller is also expected to own the
+ * lifetime of the memdev registration associated with the endpoint to
+ * pin the decoder registered as well.
+ */
+struct cxl_endpoint_decoder *cxl_request_dpa(struct cxl_memdev *cxlmd,
+					     bool is_ram,
+					     resource_size_t alloc)
+{
+	struct cxl_port *endpoint = cxlmd->endpoint;
+	struct cxl_endpoint_decoder *cxled;
+	enum cxl_partition_mode mode;
+	struct device *cxled_dev;
+	int rc;
+
+	if (!IS_ALIGNED(alloc, SZ_256M))
+		return ERR_PTR(-EINVAL);
+
+	down_read(&cxl_dpa_rwsem);
+	cxled_dev = device_find_child(&endpoint->dev, NULL, find_free_decoder);
+	up_read(&cxl_dpa_rwsem);
+
+	if (!cxled_dev)
+		return ERR_PTR(-ENXIO);
+
+	cxled = to_cxl_endpoint_decoder(cxled_dev);
+
+	if (!cxled) {
+		rc = -ENODEV;
+		goto err;
+	}
+
+	if (is_ram)
+		mode = CXL_PARTMODE_RAM;
+	else
+		mode = CXL_PARTMODE_PMEM;
+
+	rc = cxl_dpa_set_part(cxled, mode);
+	if (rc)
+		goto err;
+
+	rc = cxl_dpa_alloc(cxled, alloc);
+	if (rc)
+		goto err;
+
+	return cxled;
+err:
+	put_device(cxled_dev);
+	return ERR_PTR(rc);
+}
+EXPORT_SYMBOL_NS_GPL(cxl_request_dpa, "CXL");
+
 static void cxld_set_interleave(struct cxl_decoder *cxld, u32 *ctrl)
 {
 	u16 eig;
diff --git a/include/cxl/cxl.h b/include/cxl/cxl.h
index a098b4e26980..22061646b147 100644
--- a/include/cxl/cxl.h
+++ b/include/cxl/cxl.h
@@ -7,6 +7,7 @@ 
 #include <linux/cdev.h>
 #include <linux/node.h>
 #include <linux/ioport.h>
+#include <linux/range.h>
 #include <cxl/mailbox.h>
 
 /*
@@ -256,4 +257,8 @@  struct cxl_root_decoder *cxl_get_hpa_freespace(struct cxl_memdev *cxlmd,
 					       unsigned long flags,
 					       resource_size_t *max);
 void cxl_put_root_decoder(struct cxl_root_decoder *cxlrd);
+struct cxl_endpoint_decoder *cxl_request_dpa(struct cxl_memdev *cxlmd,
+					     bool is_ram,
+					     resource_size_t alloc);
+int cxl_dpa_free(struct cxl_endpoint_decoder *cxled);
 #endif