[PATCH v8 08/21] dt / chosen: Add linux,uefi-stub-generated-dtb property

[hanjun.guo@linaro.org (Hanjun Guo)]

On 2015?02?07? 13:03, Ard Biesheuvel wrote:
> On 7 February 2015 at 03:36, Hanjun Guo <hanjun.guo@linaro.org> wrote:
>> On 2015?02?06? 18:34, G Gregory wrote:
>> [...]
>>
>>>>>>>
>>>>>>> --------------------------------------------------------------------------------
>>>>>>>    linux,uefi-stub-kern-ver  | string | Copy of linux_banner from
>>>>>>> build.
>>>>>>>
>>>>>>> --------------------------------------------------------------------------------
>>>>>>> +linux,uefi-stub-generated-dtb  | bool | Indication for no DTB
>>>>>>> provided by
>>>>>>> +                        |      | firmware.
>>>>>>>
>>>>>>> +--------------------------------------------------------------------------------
>>>>>>
>>>>>>
>>>>>> Apologies for the late bikeshedding, but the discussion on this topic
>>>>>> previsously was lively enough that I thought I'd let it die down a bit
>>>>>> before seeing if I had anything to add.
>>>>>>
>>>>>> That, and I just realised something:
>>>>>> One alternative to this added DT entry is that we could treat the
>>>>>> absence of a registered UEFI configuration table as the indication
>>>>>> that no HW description was provided from firmware, since the stub does
>>>>>> not call InstallConfigurationTable() on the DT it generates. This does
>>>>>> move the ability to detect to after efi_init(), but this should be
>>>>>> fine for ACPI-purposes.
>>>>>>
>>>>> That would not work as expected in the kexec/Xen use case though as they
>>>>> may genuinely boot with DT from an ACPI host without UEFI.
>>>>
>>>>
>>>> I'm a little concerned by this case. How do we intend to pass stuff from
>>>> Xen to the kernel in this case? When we initially discussed the stub
>>>> prior to merging, we weren't quite sure if ACPI without UEFI was
>>>> entirely safe.
>>>>
>>>> The linux,uefi-stub-kern-ver property was originally intended as a
>>>> sanity-check feature to ensure nothing (including Xen) masqueraded as
>>>> the stub, but for some reason the actual sanity check was never
>>>> implemented.
>>>>
>>>>>> If that is deemed undesirable, I would still prefer Catalin's
>>>>>> suggested name ("linux,bare-dtb"), which describes the state rather
>>>>>> than the route we took to get there.
>>>>>>
>>>>> I agree.
>>>>
>>>>
>>>> I guess this would be ok, though it would be nice to know which agent
>>>> generated the DTB.
>>>>
>>>
>>> The most obvious scheme then is
>>>
>>> linux,bare-dtb = "uefi-stub";
>>>
>>> otherwise we generate a new binding for every component in the boot path.
>>
>>
>> Leif, Mark, any comments on this?
>>
>
> As far as I remember, we did not finalize the decision to go with a
> stub generated property instead of some other means to infer that the
> device tree is not suitable for booting and ACPI should be preferred.
>
> We will be discussing the 'stub<->kernel interface as a boot protocol'
> topic this week at Connect, so let's discuss it in that context before
> signing off on patches like these.

OK, see you guys in Hongkong.

Thanks
Hanjun