cxl: Add support to handle user feature commands for get feature

Add helper function to parse the user data from fwctl RPC ioctl and
send the parsed input parameters to cxl_get_feature() call.

Link: https://patch.msgid.link/r/20250307205648.1021626-5-dave.jiang@intel.com
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Li Ming <ming.li@zohomail.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

Author: davejiang

drivers/cxl/core/features.c

@@ -427,6 +427,47 @@ static void *cxlctl_get_supported_features(struct cxl_features_state *cxlfs,
 	return no_free_ptr(rpc_out);
 }
 
+static void *cxlctl_get_feature(struct cxl_features_state *cxlfs,
+				const struct fwctl_rpc_cxl *rpc_in,
+				size_t *out_len)
+{
+	struct cxl_mailbox *cxl_mbox = &cxlfs->cxlds->cxl_mbox;
+	const struct cxl_mbox_get_feat_in *feat_in;
+	u16 offset, count, return_code;
+	size_t out_size = *out_len;
+
+	if (rpc_in->op_size != sizeof(*feat_in))
+		return ERR_PTR(-EINVAL);
+
+	feat_in = &rpc_in->get_feat_in;
+	offset = le16_to_cpu(feat_in->offset);
+	count = le16_to_cpu(feat_in->count);
+
+	if (!count)
+		return ERR_PTR(-EINVAL);
+
+	struct fwctl_rpc_cxl_out *rpc_out __free(kvfree) =
+		kvzalloc(out_size, GFP_KERNEL);
+	if (!rpc_out)
+		return ERR_PTR(-ENOMEM);
+
+	out_size = cxl_get_feature(cxl_mbox, &feat_in->uuid,
+				   feat_in->selection, rpc_out->payload,
+				   count, offset, &return_code);
+	*out_len = sizeof(struct fwctl_rpc_cxl_out);
+	if (!out_size) {
+		rpc_out->size = 0;
+		rpc_out->retval = return_code;
+		return no_free_ptr(rpc_out);
+	}
+
+	rpc_out->size = out_size;
+	rpc_out->retval = CXL_MBOX_CMD_RC_SUCCESS;
+	*out_len += out_size;
+
+	return no_free_ptr(rpc_out);
+}
+
 static bool cxlctl_validate_hw_command(struct cxl_features_state *cxlfs,
 				       const struct fwctl_rpc_cxl *rpc_in,
 				       enum fwctl_rpc_scope scope,
@@ -436,6 +477,7 @@ static bool cxlctl_validate_hw_command(struct cxl_features_state *cxlfs,
 
 	switch (opcode) {
 	case CXL_MBOX_OP_GET_SUPPORTED_FEATURES:
+	case CXL_MBOX_OP_GET_FEATURE:
 		if (cxl_mbox->feat_cap < CXL_FEATURES_RO)
 			return false;
 		if (scope >= FWCTL_RPC_CONFIGURATION)
@@ -453,6 +495,8 @@ static void *cxlctl_handle_commands(struct cxl_features_state *cxlfs,
 	switch (opcode) {
 	case CXL_MBOX_OP_GET_SUPPORTED_FEATURES:
 		return cxlctl_get_supported_features(cxlfs, rpc_in, out_len);
+	case CXL_MBOX_OP_GET_FEATURE:
+		return cxlctl_get_feature(cxlfs, rpc_in, out_len);
 	default:
 		return ERR_PTR(-EOPNOTSUPP);
 	}

include/uapi/fwctl/cxl.h

@@ -18,6 +18,7 @@
  * @op_size: Size of input payload.
  * @reserved1: Reserved. Must be 0s.
  * @get_sup_feats_in: Get Supported Features input
+ * @get_feat_in: Get Feature input
  */
 struct fwctl_rpc_cxl {
 	__struct_group(fwctl_rpc_cxl_hdr, hdr, /* no attrs */,
@@ -26,21 +27,28 @@ struct fwctl_rpc_cxl {
 		__u32 op_size;
 		__u32 reserved1;
 	);
-	struct cxl_mbox_get_sup_feats_in get_sup_feats_in;
+	union {
+		struct cxl_mbox_get_sup_feats_in get_sup_feats_in;
+		struct cxl_mbox_get_feat_in get_feat_in;
+	};
 };
 
 /**
  * struct fwctl_rpc_cxl_out - ioctl(FWCTL_RPC) output for CXL
  * @size: Size of the output payload
  * @retval: Return value from device
  * @get_sup_feats_out: Get Supported Features output
+ * @payload: raw byte stream of payload
  */
 struct fwctl_rpc_cxl_out {
 	__struct_group(fwctl_rpc_cxl_out_hdr, hdr, /* no attrs */,
 		__u32 size;
 		__u32 retval;
 	);
-	struct cxl_mbox_get_sup_feats_out get_sup_feats_out;
+	union {
+		struct cxl_mbox_get_sup_feats_out get_sup_feats_out;
+		__DECLARE_FLEX_ARRAY(__u8, payload);
+	};
 };
 
 #endif