cxl/mbox: Add GET_FEATURE mailbox command

Add support for GET_FEATURE mailbox command.

CXL spec r3.2 section 8.2.9.6 describes optional device specific features.
The settings of a feature can be retrieved using Get Feature command.
CXL spec r3.2 section 8.2.9.6.2 describes Get Feature command.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Li Ming <ming.li@zohomail.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Shiju Jose <shiju.jose@huawei.com>
Link: https://patch.msgid.link/20250220194438.2281088-5-dave.jiang@intel.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>

drivers/cxl/core/core.h

@@ -117,4 +117,11 @@ bool cxl_need_node_perf_attrs_update(int nid);
 int cxl_port_get_switch_dport_bandwidth(struct cxl_port *port,
 					struct access_coordinate *c);
 
+#ifdef CONFIG_CXL_FEATURES
+size_t cxl_get_feature(struct cxl_mailbox *cxl_mbox, const uuid_t *feat_uuid,
+		       enum cxl_get_feat_selection selection,
+		       void *feat_out, size_t feat_out_size, u16 offset,
+		       u16 *return_code);
+#endif
+
 #endif /* __CXL_CORE_H__ */

drivers/cxl/core/features.c

@@ -4,6 +4,7 @@
 #include <cxl/mailbox.h>
 #include <cxl/features.h>
 #include "cxl.h"
+#include "core.h"
 #include "cxlmem.h"
 
 inline struct cxl_features_state *to_cxlfs(struct cxl_dev_state *cxlds)
@@ -173,3 +174,52 @@ int devm_cxl_setup_features(struct cxl_dev_state *cxlds)
 	return devm_add_action_or_reset(cxlds->dev, free_cxlfs, no_free_ptr(cxlfs));
 }
 EXPORT_SYMBOL_NS_GPL(devm_cxl_setup_features, "CXL");
+
+size_t cxl_get_feature(struct cxl_mailbox *cxl_mbox, const uuid_t *feat_uuid,
+		       enum cxl_get_feat_selection selection,
+		       void *feat_out, size_t feat_out_size, u16 offset,
+		       u16 *return_code)
+{
+	size_t data_to_rd_size, size_out;
+	struct cxl_mbox_get_feat_in pi;
+	struct cxl_mbox_cmd mbox_cmd;
+	size_t data_rcvd_size = 0;
+	int rc;
+
+	if (return_code)
+		*return_code = CXL_MBOX_CMD_RC_INPUT;
+
+	if (!feat_out || !feat_out_size)
+		return 0;
+
+	size_out = min(feat_out_size, cxl_mbox->payload_size);
+	uuid_copy(&pi.uuid, feat_uuid);
+	pi.selection = selection;
+	do {
+		data_to_rd_size = min(feat_out_size - data_rcvd_size,
+				      cxl_mbox->payload_size);
+		pi.offset = cpu_to_le16(offset + data_rcvd_size);
+		pi.count = cpu_to_le16(data_to_rd_size);
+
+		mbox_cmd = (struct cxl_mbox_cmd) {
+			.opcode = CXL_MBOX_OP_GET_FEATURE,
+			.size_in = sizeof(pi),
+			.payload_in = &pi,
+			.size_out = size_out,
+			.payload_out = feat_out + data_rcvd_size,
+			.min_out = data_to_rd_size,
+		};
+		rc = cxl_internal_send_cmd(cxl_mbox, &mbox_cmd);
+		if (rc < 0 || !mbox_cmd.size_out) {
+			if (return_code)
+				*return_code = mbox_cmd.return_code;
+			return 0;
+		}
+		data_rcvd_size += mbox_cmd.size_out;
+	} while (data_rcvd_size < feat_out_size);
+
+	if (return_code)
+		*return_code = CXL_MBOX_CMD_RC_SUCCESS;
+
+	return data_rcvd_size;
+}

include/cxl/features.h

@@ -67,6 +67,29 @@ struct cxl_mbox_get_sup_feats_out {
 	struct cxl_feat_entry ents[] __counted_by_le(num_entries);
 } __packed;
 
+/*
+ * Get Feature CXL spec r3.2 Spec 8.2.9.6.2
+ */
+
+/*
+ * Get Feature input payload
+ * CXL spec r3.2 section 8.2.9.6.2 Table 8-99
+ */
+struct cxl_mbox_get_feat_in {
+	uuid_t uuid;
+	__le16 offset;
+	__le16 count;
+	u8 selection;
+}  __packed;
+
+/* Selection field for 'struct cxl_mbox_get_feat_in' */
+enum cxl_get_feat_selection {
+	CXL_GET_FEAT_SEL_CURRENT_VALUE,
+	CXL_GET_FEAT_SEL_DEFAULT_VALUE,
+	CXL_GET_FEAT_SEL_SAVED_VALUE,
+	CXL_GET_FEAT_SEL_MAX
+};
+
 /**
  * struct cxl_features_state - The Features state for the device
  * @cxlds: Pointer to CXL device state
@@ -82,6 +105,7 @@ struct cxl_features_state {
 	} *entries;
 };
 
+struct cxl_mailbox;
 #ifdef CONFIG_CXL_FEATURES
 inline struct cxl_features_state *to_cxlfs(struct cxl_dev_state *cxlds);
 int devm_cxl_setup_features(struct cxl_dev_state *cxlds);