Re: [PATCH v7] xen/arm: pci: introduce PCI_PASSTHROUGH Kconfig option

[Stewart Hildebrand <stewart.hildebrand@xxxxxxx>]

On 6/12/25 10:58, Jan Beulich wrote:
> On 12.06.2025 15:39, Stewart Hildebrand wrote:
>> On 6/11/25 01:23, Jan Beulich wrote:
>>> On 10.06.2025 19:46, Stewart Hildebrand wrote:
>>>> --- a/xen/arch/arm/Kconfig
>>>> +++ b/xen/arch/arm/Kconfig
>>>> @@ -258,6 +258,16 @@ config PARTIAL_EMULATION
>>>>  
>>>>  source "arch/arm/firmware/Kconfig"
>>>>  
>>>> +config PCI_PASSTHROUGH
>>>> +  bool "PCI passthrough" if EXPERT
>>>> +  depends on ARM_64
>>>> +  select HAS_PCI
>>>> +  select HAS_VPCI
>>>> +  select HAS_VPCI_GUEST_SUPPORT
>>>
>>> What about HAS_PASSTHROUGH? Seeing that being selected by MMU, what about
>>> that connection here?
>>
>> Hm, yes. I'm not sure if depends or select would be better?
>>
>>      depends on ARM_64 && HAS_PASSTHROUGH
>>
>> or
>>
>>      select HAS_PASSTHROUGH
> 
> Actually, thinking of it: HAS_* shouldn't be selected based on user choices,
> imo. Perhaps unless the HAS_* is a sub-feature of the dependent (as in e.g.
> "select HAS_VPCI if HVM" as we have it for x86). In which case all the
> select-s here might be wrong to use.

How about something like this:

diff --git a/xen/arch/arm/Kconfig b/xen/arch/arm/Kconfig
index 3f25da3ca5fd..95a2cd3d006d 100644
--- a/xen/arch/arm/Kconfig
+++ b/xen/arch/arm/Kconfig
@@ -8,6 +8,8 @@ config ARM_64
        depends on !ARM_32
        select 64BIT
        select HAS_FAST_MULTIPLY
+       select HAS_VPCI_GUEST_SUPPORT if PCI_PASSTHROUGH
+       select HAS_PASSTHROUGH if PCI_PASSTHROUGH
 
 config ARM
        def_bool y
@@ -258,6 +260,12 @@ config PARTIAL_EMULATION
 
 source "arch/arm/firmware/Kconfig"
 
+config PCI_PASSTHROUGH
+       bool "PCI passthrough" if EXPERT
+       depends on ARM_64
+       help
+         This option enables PCI device passthrough
+
 endmenu
 
 menu "ARM errata workaround via the alternative framework"
diff --git a/xen/drivers/Kconfig b/xen/drivers/Kconfig
index 20050e9bb8b3..0c376704ddc9 100644
--- a/xen/drivers/Kconfig
+++ b/xen/drivers/Kconfig
@@ -13,6 +13,7 @@ source "drivers/pci/Kconfig"
 source "drivers/video/Kconfig"
 
 config HAS_VPCI
+       select HAS_PCI
        bool
 
 config HAS_VPCI_GUEST_SUPPORT