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Re: [PATCH v2 10/11] vpci: Add initial support for virtual PCI bus topology

  • To: Oleksandr Andrushchenko <Oleksandr_Andrushchenko@xxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Wed, 29 Sep 2021 14:54:42 +0200
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  • Cc: "julien@xxxxxxx" <julien@xxxxxxx>, "sstabellini@xxxxxxxxxx" <sstabellini@xxxxxxxxxx>, Oleksandr Tyshchenko <Oleksandr_Tyshchenko@xxxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Artem Mygaiev <Artem_Mygaiev@xxxxxxxx>, "roger.pau@xxxxxxxxxx" <roger.pau@xxxxxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Rahul Singh <rahul.singh@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>
  • Delivery-date: Wed, 29 Sep 2021 12:55:06 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 29.09.2021 13:56, Oleksandr Andrushchenko wrote:
> On 29.09.21 12:09, Jan Beulich wrote:
>> On 29.09.2021 11:03, Oleksandr Andrushchenko wrote:
>>> Sorry for top posting, but this is a general question on this 
>>> patch/functionality.
>>> Do you see we need to gate all this with CONFIG_HAS_VPCI_GUEST_SUPPORT
>>> as this renders in somewhat dead code for x86 for now? I do think this still
>>> needs to be in the common code though.
>> I agree it wants to live in common code, but I'd still like the code to
>> not bloat x86 binaries. Hence yes, I think there want to be
>> "if ( !IS_ENABLED() )" early bailout paths or, whenever this isn't
>> possible without breaking the build, respective #ifdef-s.
> Then it needs to be defined as (xen/drivers/Kconfig):
>      # vPCI guest support is only enabled for Arm now
>      def_bool y if ARM
>      depends on HAS_VPCI
> Because it needs to be defined as "y" for Arm with vPCI support.
> Otherwise it breaks the PCI passthrough feature, e.g. it compiles,
> but the resulting binary behaves wrong.
> Do you see this as an acceptable solution?

Like all (or at least the majority) of other HAS_*, it ought to be
"select"-ed (by arm/Kconfig). Is there a reason this isn't possible?
(I don't mind the "depends on", as long as it's clear that it exists
solely to allow kconfig to warn about bogus "select"s.)




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