On Monday 15 December 2014 19:18:16 Al Stone wrote:

Below is what we currently know about; very brief notes on status are included. The TL;DR versions of the TODO list and the current status can be found at:

https://wiki.linaro.org/LEG/Engineering/Kernel/ACPI/CoreUpstreamNotes

and I'll do my best to kept that up to date.

Thanks. Any and all feedback is greatly appreciated.

Thanks for keeping the list up to date!

TODO List for ACPI on arm64:

1. Define how Aarch64 OS identifies itself to firmware.
   • Problem:
     • _OSI method is demonstrably unreliable. On x86 Linux claims to be Windows
     • Proposal to use _OSC method as replacement is complicated and creates an explosion of combinations
   • Solution:
     • Draft and propose OS identification rules to ABST and ASWG for inclusion in ACPI spec.
     • Draft and propose recommended practice for current ACPI 5.1 spec platforms.
   • Status: Little progress, still under investigation

I must have missed the problem with _OSC, it sounded like it was good enough, but I have no clue about the details.

2. Linux must choose DT booting by default when offered both ACPI and DT on arm64

   • DONE

3. Linux UEFI/ACPI testing tools must be made available

   • Problem:
     • Hardware/Firmware vendors do not have tools to test Linux compatibility.
     • Common problems go undetected if not tested for.
   • Solution:
     • Port FWTS tool and LuvOS distribution to AArch64
     • Make LuvOS images readily available
     • Require hardware vendors to actively test against old and new kernels.
   • Status: LuvOS and FWTS ported to arm64 and running; patches being mainlined; additional test cases being written.

Ah, nice!

4. Set clear expectations for those providing ACPI for use with Linux
   • Problem:
     • Hardware/Firmware vendors can and will create ACPI tables that cannot be used by Linux without some guidance
     • Kernel developers cannot determine whether the kernel or firmware is broken without knowing what the firmware should do
   • Solution: document the expectations, and iterate as needed. Enforce when we must.
   • Status: initial kernel text available; AMD has offered to make their guidance document generic; firmware summit planned for deeper discussions.

After seeing the AMD patches, I would add to this point that we need to find a way to come up with shared bindings for common hardware such as the ARM pl011/pl022/pl061/pl330 IP blocks or the designware i2c/spi/usb3/ahci blocks.

What I remember from this item on your list is actually a different problem: We need to define more clearly what kinds of machines we would expect ACPI support for and which machines we would not.

Fine-grained clock support is one such example: if anybody needs to expose that through a clock driver in the kernel, we need to be very clear that we will not support that kind of machine through ACPI, so we don't get developers building BIOS images that will never be supported. Other examples would be non-compliant PCI hosts or machines that are not covered by SBSA.

5. Demonstrate the ACPI core patches work
   • Problem: how can we be sure the patches work?
   • Solution: verify the patches on arm64 server platforms
   • Status:
     • ACPI core works on at least the Foundation model, Juno, APM Mustang, and AMD Seattle
     • FWTS results will be published as soon as possible

I think the problem is to a lesser degree the verification of the patches, but to have a patch set that demonstrates /how/ everything can work, and what the possible limitations are. I would not worry about any bugs that might keep the system from working properly, as long as you can show that there is a plan to make that work.

Out of the four platforms you list, I think we have concluded that three of them are not appropriate for use with ACPI, but in order to do that, we needed to review the patches and pinpoint specific issues so we could avoid just exchanging different opinions on the matter of it "works" or not.

6. How does the kernel handle_DSD usage?
   • Problem:
     • _DSD defines key-value properties in the DT style. How do we ensure _DSD bindings are well defined?
     • How do we ensure DT and _DSD bindings remain consistent with each other?
   • Solution: public documentation for all bindings, and a process for defining them
   • Status: proposal to require patch authors to point at public binding documentation; kernel Documentation/devicetree/bindings remains the default if no other location exists; UEFI forum has set up a binding repository.

I think we also need to make a decision here on whether we want to use PRP0001 devices on ARM64 servers, and to what degree. I would prefer if we could either make them required for any devices that already have a DT binding and that are not part of the official ACPI spec, or we decide to not use them at all and make any PRP0001 usage a testcase failure.

7. Why is ACPI required?
   • Problem:
     • arm64 maintainers still haven't been convinced that ACPI is necessary.
     • Why do hardware and OS vendors say ACPI is required?
   • Status: Al & Grant collecting statements from OEMs to be posted publicly early in the new year; firmware summit for broader discussion planned.

I was particularly hoping to see better progress on this item. It really shouldn't be that hard to explain why someone wants this feature.

8. Platform support patches need review
   • Problem: the core Aarch64 patches have been reviewed and are in good shape, but there is not yet a good example of server platform support patches that use them.
   • Solution: Post *good* patches for multiple ACPI platforms
   • Status: first version for AMD Seattle has been posted to the public linaro-acpi mailing list for initial review (thanks, Arnd), refined versions to be posted to broader lists after a few iterations for basic cleanup

Arnd