+/**
+ * Perform read access to the registers. Reads data from register
+ * and writes ones to the specified buffer.
+ *
+ * @param[in] ctx
+ * Context returned from mlx5 open_device() glue function.
+ * @param[in] reg_id
+ * Register identifier according to the PRM.
+ * @param[in] arg
+ * Register access auxiliary parameter according to the PRM.
+ * @param[out] data
+ * Pointer to the buffer to store read data.
+ * @param[in] dw_cnt
+ * Buffer size in double words.
+ *
+ * @return
+ * 0 on success, a negative value otherwise.
+ */
+int
+mlx5_devx_cmd_register_read(void *ctx, uint16_t reg_id, uint32_t arg,
+ uint32_t *data, uint32_t dw_cnt)
+{
+ uint32_t in[MLX5_ST_SZ_DW(access_register_in)] = {0};
+ uint32_t out[MLX5_ST_SZ_DW(access_register_out) +
+ MLX5_ACCESS_REGISTER_DATA_DWORD_MAX] = {0};
+ int status, rc;
+
+ MLX5_ASSERT(data && dw_cnt);
+ MLX5_ASSERT(dw_cnt <= MLX5_ACCESS_REGISTER_DATA_DWORD_MAX);
+ if (dw_cnt > MLX5_ACCESS_REGISTER_DATA_DWORD_MAX) {
+ DRV_LOG(ERR, "Not enough buffer for register read data");
+ return -1;
+ }
+ MLX5_SET(access_register_in, in, opcode,
+ MLX5_CMD_OP_ACCESS_REGISTER_USER);
+ MLX5_SET(access_register_in, in, op_mod,
+ MLX5_ACCESS_REGISTER_IN_OP_MOD_READ);
+ MLX5_SET(access_register_in, in, register_id, reg_id);
+ MLX5_SET(access_register_in, in, argument, arg);
+ rc = mlx5_glue->devx_general_cmd(ctx, in, sizeof(in), out,
+ MLX5_ST_SZ_DW(access_register_out) *
+ sizeof(uint32_t) + dw_cnt);
+ if (rc)
+ goto error;
+ status = MLX5_GET(access_register_out, out, status);
+ if (status) {
+ int syndrome = MLX5_GET(access_register_out, out, syndrome);
+
+ DRV_LOG(DEBUG, "Failed to access NIC register 0x%X, "
+ "status %x, syndrome = %x",
+ reg_id, status, syndrome);
+ return -1;
+ }
+ memcpy(data, &out[MLX5_ST_SZ_DW(access_register_out)],
+ dw_cnt * sizeof(uint32_t));
+ return 0;
+error:
+ rc = (rc > 0) ? -rc : rc;
+ return rc;
+}
+