Re: [PATCH 06/19] xen: Clean up asm-generic/device.h

[Jan Beulich <jbeulich@xxxxxxxx>]

On 05.06.2025 16:15, Alejandro Vallejo wrote:
> On Mon Jun 2, 2025 at 4:24 PM CEST, Jan Beulich wrote:
>> On 02.06.2025 16:19, Alejandro Vallejo wrote:
>>> On Mon Jun 2, 2025 at 9:51 AM CEST, Jan Beulich wrote:
>>>> On 30.05.2025 14:02, Alejandro Vallejo wrote:
>>>>> --- a/xen/include/asm-generic/device.h
>>>>> +++ b/xen/include/asm-generic/device.h
>>>>> @@ -6,9 +6,7 @@
>>>>>  
>>>>>  enum device_type
>>>>>  {
>>>>> -#ifdef CONFIG_HAS_DEVICE_TREE
>>>>>      DEV_DT,
>>>>> -#endif
>>>>
>>>> Why would this enumerator need exposing on a non-DT arch? In fact I would 
>>>> have
>>>> hoped for ...
>>>
>>> A non-DT arch would not include this. x86 doesn't.
>>
>> Both here and ...
>>
>>>>>      DEV_PCI
>>>>
>>>> ... this to be hidden for arch-es not supporting PCI.
>>>>
>>>> Similar concerns elsewhere in this change.
>>>
>>> This file is exclusively used by arches supporting DT to abstract away where
>>> the device came from. x86 does not use it at all, and while it wouldn't be
>>> impossible to compile-out DEV_PCI, it would needlessly pollute the codebase 
>>> with
>>> no measurable gain, because the abstractions still need to stay.
>>
>> ... here: In "xen/include/asm-generic/device.h" there's nothing at all saying
>> that this file is a DT-only one. Instead there is something in there saying
>> that it's suitable to use in the entirely "generic" case.
>>
>> Jan
> 
> Try to use it from x86 and observe the build system catch fire. It could be 
> made
> to not go on fire, but it implies heavy refactoring in x86 (particularly IOMMU
> code) for no good reason because there's no devices in a DTB to disambiguate.
> 
> How about adding this to the top of the header?
> 
> ```
>  /*
>   * This header helps DTB-based architectures abstract away where a particular
>   * device comes from; be it the DTB itself or enumerated on a PCI bus. 
>   */
> 
>   [snip]
> 
>  #ifndef CONFIG_HAS_DEVICE_TREE
>  #error "Header meant to be used exclusively by DTB-base architectures."
>  #endif
> ```

Might be fine, together with giving the file a name somewhat referring to DT.

Jan