RE: [PATCH 20/37] xen: introduce CONFIG_EFI to stub API for non-EFI architecture

[Wei Chen <Wei.Chen@arm.com>]

> -----Original Message-----
> From: Jan Beulich <jbeulich@suse.com>
> Sent: 2021年9月28日 16:03
> To: Stefano Stabellini <sstabellini@kernel.org>; Wei Chen
> <Wei.Chen@arm.com>
> Cc: xen-devel@lists.xenproject.org; julien@xen.org; Bertrand Marquis
> <Bertrand.Marquis@arm.com>
> Subject: Re: [PATCH 20/37] xen: introduce CONFIG_EFI to stub API for non-
> EFI architecture
> 
> On 28.09.2021 07:01, Stefano Stabellini wrote:
> > On Tue, 28 Sep 2021, Wei Chen wrote:
> >>> -----Original Message-----
> >>> From: Stefano Stabellini <sstabellini@kernel.org>
> >>> Sent: 2021年9月28日 9:00
> >>> To: Wei Chen <Wei.Chen@arm.com>
> >>> Cc: Jan Beulich <jbeulich@suse.com>; xen-devel@lists.xenproject.org;
> >>> julien@xen.org; Bertrand Marquis <Bertrand.Marquis@arm.com>; Stefano
> >>> Stabellini <sstabellini@kernel.org>
> >>> Subject: RE: [PATCH 20/37] xen: introduce CONFIG_EFI to stub API for
> non-
> >>> EFI architecture
> >>>
> >>> On Mon, 27 Sep 2021, Wei Chen wrote:
> >>>>> -----Original Message-----
> >>>>> From: Xen-devel <xen-devel-bounces@lists.xenproject.org> On Behalf
> Of
> >>> Wei
> >>>>> Chen
> >>>>> Sent: 2021年9月26日 18:25
> >>>>> To: Jan Beulich <jbeulich@suse.com>
> >>>>> Cc: xen-devel@lists.xenproject.org; julien@xen.org; Bertrand Marquis
> >>>>> <Bertrand.Marquis@arm.com>; Stefano Stabellini
> <sstabellini@kernel.org>
> >>>>> Subject: RE: [PATCH 20/37] xen: introduce CONFIG_EFI to stub API for
> >>> non-
> >>>>> EFI architecture
> >>>>>
> >>>>> Hi Jan,
> >>>>>
> >>>>>> -----Original Message-----
> >>>>>> From: Xen-devel <xen-devel-bounces@lists.xenproject.org> On Behalf
> >>> Of
> >>>>> Jan
> >>>>>> Beulich
> >>>>>> Sent: 2021年9月24日 18:49
> >>>>>> To: Wei Chen <Wei.Chen@arm.com>
> >>>>>> Cc: xen-devel@lists.xenproject.org; julien@xen.org; Bertrand
> Marquis
> >>>>>> <Bertrand.Marquis@arm.com>; Stefano Stabellini
> >>> <sstabellini@kernel.org>
> >>>>>> Subject: Re: [PATCH 20/37] xen: introduce CONFIG_EFI to stub API
> for
> >>>>> non-
> >>>>>> EFI architecture
> >>>>>>
> >>>>>> On 24.09.2021 12:31, Wei Chen wrote:
> >>>>>>>> From: Jan Beulich <jbeulich@suse.com>
> >>>>>>>> Sent: 2021年9月24日 15:59
> >>>>>>>>
> >>>>>>>> On 24.09.2021 06:34, Wei Chen wrote:
> >>>>>>>>>> From: Stefano Stabellini <sstabellini@kernel.org>
> >>>>>>>>>> Sent: 2021年9月24日 9:15
> >>>>>>>>>>
> >>>>>>>>>> On Thu, 23 Sep 2021, Wei Chen wrote:
> >>>>>>>>>>> --- a/xen/common/Kconfig
> >>>>>>>>>>> +++ b/xen/common/Kconfig
> >>>>>>>>>>> @@ -11,6 +11,16 @@ config COMPAT
> >>>>>>>>>>>  config CORE_PARKING
> >>>>>>>>>>>  	bool
> >>>>>>>>>>>
> >>>>>>>>>>> +config EFI
> >>>>>>>>>>> +	bool
> >>>>>>>>>>
> >>>>>>>>>> Without the title the option is not user-selectable (or de-
> >>>>>> selectable).
> >>>>>>>>>> So the help message below can never be seen.
> >>>>>>>>>>
> >>>>>>>>>> Either add a title, e.g.:
> >>>>>>>>>>
> >>>>>>>>>> bool "EFI support"
> >>>>>>>>>>
> >>>>>>>>>> Or fully make the option a silent option by removing the help
> >>> text.
> >>>>>>>>>
> >>>>>>>>> OK, in current Xen code, EFI is unconditionally compiled. Before
> >>>>>>>>> we change related code, I prefer to remove the help text.
> >>>>>>>>
> >>>>>>>> But that's not true: At least on x86 EFI gets compiled depending
> >>> on
> >>>>>>>> tool chain capabilities. Ultimately we may indeed want a user
> >>>>>>>> selectable option here, but until then I'm afraid having this
> >>> option
> >>>>>>>> at all may be misleading on x86.
> >>>>>>>>
> >>>>>>>
> >>>>>>> I check the build scripts, yes, you're right. For x86, EFI is not
> >>> a
> >>>>>>> selectable option in Kconfig. I agree with you, we can't use
> >>> Kconfig
> >>>>>>> system to decide to enable EFI build for x86 or not.
> >>>>>>>
> >>>>>>> So how about we just use this EFI option for Arm only? Because on
> >>> Arm,
> >>>>>>> we do not have such toolchain dependency.
> >>>>>>
> >>>>>> To be honest - don't know. That's because I don't know what you
> want
> >>>>>> to use the option for subsequently.
> >>>>>>
> >>>>>
> >>>>> In last version, I had introduced an arch-helper to stub EFI_BOOT
> >>>>> in Arm's common code for Arm32. Because Arm32 doesn't support EFI.
> >>>>> So Julien suggested me to introduce a CONFIG_EFI option for non-EFI
> >>>>> supported architectures to stub in EFI layer.
> >>>>>
> >>>>> [1] https://lists.xenproject.org/archives/html/xen-devel/2021-
> >>>>> 08/msg00808.html
> >>>>>
> >>>>
> >>>> As Jan' reminded, x86 doesn't depend on Kconfig to build EFI code.
> >>>> So, if we CONFIG_EFI to stub EFI API's for x86, we will encounter
> >>>> that toolchains enable EFI, but Kconfig disable EFI. Or Kconfig
> >>>> enable EFI but toolchain doesn't provide EFI build supports. And
> >>>> then x86 could not work well.
> >>>>
> >>>> If we use CONFIG_EFI for Arm only, that means CONFIG_EFI for x86
> >>>> is off, this will also cause problem.
> >>>>
> >>>> So, can we still use previous arch_helpers to stub for Arm32?
> >>>> until x86 can use this selectable option?
> >>>
> >>> EFI doesn't have to be necessarily a user-visible option in Kconfig at
> >>> this point. I think Julien was just asking to make the #ifdef based on
> >>> a EFI-related config rather than just based CONFIG_ARM64.
> >>>
> >>> On x86 EFI is detected based on compiler support, setting
> XEN_BUILD_EFI
> >>> in xen/arch/x86/Makefile. Let's say that we keep using the same name
> >>> "XEN_BUILD_EFI" on ARM as well.
> >>>
> >>> On ARM32, XEN_BUILD_EFI should be always unset.
> >>>
> >>> On ARM64 XEN_BUILD_EFI should be always set.
> >>>
> >>> That's it, right? I'd argue that CONFIG_EFI or HAS_EFI are better
> names
> >>> than XEN_BUILD_EFI, but that's OK anyway. So for instance you can make
> >>> XEN_BUILD_EFI an invisible symbol in xen/arch/arm/Kconfig and select
> it
> >>> only on ARM64.
> >>
> >> Thanks, this is a good approach. But if we place XEN_BUILD_EFI in
> Kconfig
> >> it will be transfer to CONFIG_XEN_BUILD_EFI. How about using another
> name
> >> in Kconfig like ARM_EFI, but use CONFIG_ARM_EFI in config.h to define
> >> XEN_BUILD_EFI?
> >
> > I am OK with that. Another option is to rename XEN_BUILD_EFI to
> > CONFIG_XEN_BUILD_EFI on x86. Either way is fine by me. Jan, do you havea
> > preference?
> 
> Yes, I do: No new CONFIG_* settings please that don't originate from
> Kconfig. Hence I'm afraid this is a "no" to your suggestion.
> 
> Mid-term we should try to get rid of the remaining CONFIG_* which
> get #define-d in e.g. asm/config.h.
> 

I will do something like this: 
 - introduce an ARM_EFI invisible symbol in kconfig, selected by ARM64 only
 - use CONFIG_ARM_EFI to define XEN_BUILD_EFI in config.h

> Jan