The PCIe device DVSEC, defined in the CXL 2.0 spec, 8.1.3 is required to be implemented by CXL 2.0 endpoint devices. In preparation for consuming this information in a new cxl_mem driver, retrieve the CXL DVSEC position and warn about the implications of not finding it. Allow for mailbox operation even if the CXL DVSEC is missing. Signed-off-by: Ben Widawsky <ben.widawsky@intel.com> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com> Link: https://lore.kernel.org/r/164375309615.513620.7874131241128599893.stgit@dwillia2-desk3.amr.corp.intel.com Signed-off-by: Dan Williams <dan.j.williams@intel.com>