[PATCH v20 13/22] cxl: Define a driver interface for DPA allocation

alejandro.lucero-palau
2025-11-10T15:37:44Z

From: Alejandro Lucero <alucerop@amd.com>

Region creation involves finding available DPA (device-physical-address)
capacity to map into HPA (host-physical-address) space.

In order to support CXL Type2 devices, 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/168592158743.1948938.7622563891193802610.stgit@dwillia2-xfh.jf.intel.com/

Signed-off-by: Alejandro Lucero <alucerop@amd.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
---
drivers/cxl/core/hdm.c | 84 ++++++++++++++++++++++++++++++++++++++++++
drivers/cxl/cxl.h | 1 +
include/cxl/cxl.h | 5 +++
3 files changed, 90 insertions(+)

diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
index d3a094ca01ad..88c8d14b8a63 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"
@@ -546,6 +547,12 @@ bool cxl_resource_contains_addr(const struct resource *res, const resource_size_
return resource_contains(res, &_addr);
}

+/**
+ * cxl_dpa_free - release DPA (Device Physical Address)
+ * @cxled: endpoint decoder linked to the DPA
+ *
+ * Returns 0 or error.
+ */
int cxl_dpa_free(struct cxl_endpoint_decoder *cxled)
{
struct cxl_port *port = cxled_to_port(cxled);
@@ -572,6 +579,7 @@ 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)
@@ -603,6 +611,82 @@ int cxl_dpa_set_part(struct cxl_endpoint_decoder *cxled,
return 0;
}

+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);
+
+ return cxled->cxld.id == (port->hdm_end + 1);
+}
+
+static struct cxl_endpoint_decoder *
+cxl_find_free_decoder(struct cxl_memdev *cxlmd)
+{
+ struct cxl_port *endpoint = cxlmd->endpoint;
+ struct device *dev;
+
+ guard(rwsem_read)(&cxl_rwsem.dpa);
+ dev = device_find_child(&endpoint->dev, NULL,
+ find_free_decoder);
+ if (!dev)
+ return NULL;
+
+ return to_cxl_endpoint_decoder(dev);
+}
+
+/**
+ * cxl_request_dpa - search and reserve DPA given input constraints
+ * @cxlmd: memdev with an endpoint port with available decoders
+ * @mode: CXL partition mode (ram vs pmem)
+ * @alloc: dpa size required
+ *
+ * Returns a pointer to a 'struct cxl_endpoint_decoder' on success or
+ * an errno encoded pointer on failure.
+ *
+ * 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 which could not be fully
+ * 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,
+ enum cxl_partition_mode mode,
+ resource_size_t alloc)
+{
+ int rc;
+
+ if (!IS_ALIGNED(alloc, SZ_256M))
+ return ERR_PTR(-EINVAL);
+
+ struct cxl_endpoint_decoder *cxled __free(put_cxled) =
+ cxl_find_free_decoder(cxlmd);
+
+ if (!cxled)
+ return ERR_PTR(-ENODEV);
+
+ rc = cxl_dpa_set_part(cxled, mode);
+ if (rc)
+ return ERR_PTR(rc);
+
+ rc = cxl_dpa_alloc(cxled, alloc);
+ if (rc)
+ return ERR_PTR(rc);
+
+ return no_free_ptr(cxled);
+}
+EXPORT_SYMBOL_NS_GPL(cxl_request_dpa, "CXL");
+
static int __cxl_dpa_alloc(struct cxl_endpoint_decoder *cxled, u64 size)
{
struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
index 5441a296c351..06a111392c3b 100644
--- a/drivers/cxl/cxl.h
+++ b/drivers/cxl/cxl.h
@@ -640,6 +640,7 @@ struct cxl_root *find_cxl_root(struct cxl_port *port);

DEFINE_FREE(put_cxl_root, struct cxl_root *, if (_T) put_device(&_T->port.dev))
DEFINE_FREE(put_cxl_port, struct cxl_port *, if (!IS_ERR_OR_NULL(_T)) put_device(&_T->dev))
+DEFINE_FREE(put_cxled, struct cxl_endpoint_decoder *, if (!IS_ERR_OR_NULL(_T)) put_device(&_T->cxld.dev))
DEFINE_FREE(put_cxl_root_decoder, struct cxl_root_decoder *, if (!IS_ERR_OR_NULL(_T)) put_device(&_T->cxlsd.cxld.dev))
DEFINE_FREE(put_cxl_region, struct cxl_region *, if (!IS_ERR_OR_NULL(_T)) put_device(&_T->dev))

diff --git a/include/cxl/cxl.h b/include/cxl/cxl.h
index 2966b95e80a6..1cbe53ad0416 100644
--- a/include/cxl/cxl.h
+++ b/include/cxl/cxl.h
@@ -7,6 +7,7 @@

#include <linux/node.h>
#include <linux/ioport.h>
+#include <linux/range.h>
#include <cxl/mailbox.h>

/**
@@ -270,4 +271,8 @@ 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,
+ enum cxl_partition_mode mode,
+ resource_size_t alloc);
+int cxl_dpa_free(struct cxl_endpoint_decoder *cxled);
#endif /* __CXL_CXL_H__ */
--
2.34.1