Re: [PATCH] device-tree: Move Arm's static-evtchn feature to common

["Orzel, Michal" <michal.orzel@xxxxxxx>]

On 03/06/2025 09:09, Jan Beulich wrote:
> On 03.06.2025 09:06, Orzel, Michal wrote:
>>
>>
>> On 03/06/2025 09:02, Jan Beulich wrote:
>>> On 03.06.2025 08:54, Orzel, Michal wrote:
>>>>
>>>>
>>>> On 02/06/2025 10:37, Jan Beulich wrote:
>>>>> On 27.05.2025 10:21, Michal Orzel wrote:
>>>>>> There's nothing Arm specific about this feature. Move it to common as
>>>>>> part of a larger activity to commonalize device tree related features.
>>>>>> For now, select it only for ARM until others (e.g. RISC-V) verify it
>>>>>> works for them too.
>>>>>>
>>>>>> Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
>>>>>
>>>>> I realize this was already committed, but ...
>>>>>
>>>>>> --- a/xen/common/Kconfig
>>>>>> +++ b/xen/common/Kconfig
>>>>>> @@ -162,6 +162,14 @@ config STATIC_MEMORY
>>>>>>  
>>>>>>            If unsure, say N.
>>>>>>  
>>>>>> +config STATIC_EVTCHN
>>>>>> +        bool "Static event channel support on a dom0less system"
>>>>>> +        depends on DOM0LESS_BOOT && ARM
>>>>>
>>>>> ... I think we should strive to avoid such arch dependencies; they simply
>>>>> don't scale very well. Instead (if needed) HAS_* should be introduced, 
>>>>> which
>>>>> each interested arch can select. In the case here, however, perhaps
>>>>> DOM0LESS_BOOT alone would have been sufficient as a dependency?
>>>> What if e.g. RISC-V wants to enable dom0less but not static 
>>>> evtchn/memory/shmem
>>>> because there are some functions to be implemented and they don't want to 
>>>> do it
>>>> now? Protecting with just DOM0LESS_BOOT would not be sufficient here.
>>>
>>> Imo a transient(!) "depends on !RISCV" would in principle be fine, if ...
>> In this case, how can I know that upfront? When moving a feature I need to 
>> put
>> some dependencies. At that point I don't know RISCV, PPC plans.
> 
> You don't need to know this up front, do you? Neither of the two presently 
> selects
> DOM0LESS_BOOT afaict, and hence such a transient negative dependency would (if
> necessary in the first place) be added when adding such a select.
Ok, so basically this should be left to people adding support for DOM0LESS_BOOT
for other arches in the future.

There is static mem and shmem left to be moved. I think we can squeeze in a
patch removing && ARM in this case.

~Michal