# HDM Host-managed-Device-Memory[Compute Express Link Memory Devices — The Linux Kernel documentation](https://docs.kernel.org/driver-api/cxl/memory-devices.html) # DVSEC Designated Vendor-specific [Compute Express Link Memory Devices — The Linux Kernel documentation](https://docs.kernel.org/driver-api/cxl/memory-devices.html) # Shared Upstream Link Calculation For certain CXL region construction with endpoints behind CXL switches (SW) or Root Ports (RP), there is the possibility of the total bandwidth for all the endpoints behind a switch being more than the switch upstream link. A similar situation can occur within the host, upstream of the root ports. The CXL driver performs an additional pass after all the targets have arrived for a region in order to recalculate the bandwidths with possible upstream link being a limiting factor in mind.[CXL Access Coordinates Computation — The Linux Kernel documentation](https://www.kernel.org/doc/html/v6.12-rc5/driver-api/cxl/access-coordinates.html). # Mailboxes normally in CXL you have to mailbox, one for host>device the other device>host for communication