Jonathan Cameron <jonathan.came...@huawei.com> writes:
> Hi All, > > For CXL emulation we require a couple of types of memory range that > are then provided to the OS via the CEDT ACPI table. > > 1) CXL Host Bridge Structures point to CXL Host Bridge Component Registers. > Small regions for each CXL Host bridge that are mapped into the memory space. > 64k each. In theory we may have a huge number of these but in reality I > think 16 will do for any reasonable system. > > 2) CXL Fixed Memory Window Structures (CFMWS) > Large PA space ranges (multiple TB) to which various CXL devices can be > assigned > and their address decoders appropriately programmed. > Each such CFMWS will have particular characteristics such as interleaving > across > multiple host bridges. The can potentially be huge but are a system > characteristic. For emulation purposes it won't matter if they move around > dependent on what else is the machine has configured. So I'd like to > just configure their size rather than fully specify them at the command line > and possibly clash on PA space with something else. Alternatively could > leave them as fully specified at the command line (address and size) and just > error out if the hit memory already in use for something else. > > Now unfortunately there are no systems out there yet that we can just > copy the memory map from... > > Coming form an Arm background I have only a vague idea of how this should be > done for x86 so apologies if it is a stupid question. > > My current approach is to put these above device_memory and moving > the pci hole up appropriately. Which board model would be be talking about here? virt? Or maybe we need a new one? If it's virt I would look at extended_memmap which floats above the configured RAM size and means less shuffling around of the relatively crowded lower address space. I have no idea about how this is handled on x86 though. > Is that the right choice? > > On Arm I currently have the Host Bridge Structures low down in the MemMap and > the CFMWS > can go above the device memory. Comments on that also welcome. > > In Ben's RFC the host bridge component register location was marked as a TODO > and a arbitrary address used in the meantime so time to figure out how to > clean > that up. > > Thanks, > > Jonathan -- Alex Bennée
