Re: [edk2-devel] mmio mappings for runtime service

["Yao, Jiewen" <jiewen.yao@intel.com>]

The BIOS driver must set EFI_RUNTIME_MEMORY attribute for the EfiGcdMemoryTypeMemoryMappedIo region with GCD service gDS->SetMemorySpaceAttributes().
Then DXE will report EfiMemoryMappedIO with EFI_RUNTIME_MEMORY attribute in UEFI memory map.
The OS will gBS->GetMemoryMap() and assign virtual address for the MMIO, and gRT->SetVirtualAddressMap() back to the BIOS.

Finally, the BIOS driver can gRT->ConvertPointer() the MMIO physical address to virtual address, then access it at runtime.

Thank you
Yao Jiewen

> -----Original Message-----
> From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Gerd
> Hoffmann
> Sent: Monday, August 30, 2021 6:24 PM
> To: devel@edk2.groups.io
> Subject: [edk2-devel] mmio mappings for runtime service
> 
>   Hi,
> 
> What is the correct way to make sure runtime services can access
> mmio registers, i.e. that there is a mapping in the page tables
> for the mmio page needed?
> 
> Is that the job of the firmware?
> Or should the OS calling the runtime service handle that?
> In case of the latter: How does the OS figure which pages are needed?
> 
> thanks,
>   Gerd
> 
> 
> 
> 
>