On Thu, Nov 05, 2020 at 12:36:21PM +0000, Jonathan Cameron via Linaro-open-discussions wrote:

[...]

IORT - Reserve memory regions (RMR)

• Shameer gave summary

• IORT Revision E (https://developer.arm.com/documentation/den0049/latest/) introduced new node type.
• A way to describe memory regions that should have unity mapping in the SMMU.
• Use case is a PCIe RAID card that has FW that uses a pool of host memory (hidden from OS).

• Status

• Patches out for ACPICA
  • Question raised by ACPICA reviewers on whether spec is final
  • Spec appears final (Lorenzo to check) but may be minor unrelated fix in doc to come (Sami).
• Patches out for kernel on relevant lists.
  • Mail from Steven Price (Arm) - (Sami Mujawar who was on the call also involved) interested for EFI framebuffer use case.

• Open questions

• Equivalent from AMD has flag to indicate that unity mapping only needed until driver has taken over (end of kernel boot assumed). Avoids and issue of holes in address space for VMs.
  • Huawei not raising this as a requirement, but Lorenzo observed interesting and deserves discussion.

May I ask a pointer pls to relevant AMD docs and patches (if there are any) ?

Thanks, Lorenzo