Re: [PATCH v4] xen/arm: Allow QEMU platform to be built with GICv2

[Dongjiu Geng <gengdongjiu1@xxxxxxxxx>]

Bertrand Marquis <Bertrand.Marquis@xxxxxxx> 于2022年1月18日周二 16:48写道：
>
> Hi Dongju,
>
> > On 18 Jan 2022, at 08:45, Dongjiu Geng <gengdongjiu1@xxxxxxxxx> wrote:
> >
> > Julien Grall <julien@xxxxxxx> 于2022年1月17日周一 22:16写道：
> >>
> >> Hi,
> >>
> >> On 17/01/2022 10:40, Dongjiu Geng wrote:
> >>> It turns out that QEMU has been supporting GICv2 virtualization since
> >>> v3.1.0. So remove the dependencies on GICv3.
> >>
> >>
> >> Technically, the current form of CONFIG_QEMU allows the same binary to
> >> boot on QEMU with GICv2 or GICv3.
> >>
> >>> If we want to use GICv3,
> >>> we can select the QEMU_LEGACY configuration.
> >>
> >> AFAIK, GICv3 is not a legacy feature... So it feels a bit odd to name it
> >> like that (see more below).
> >
> > Legacy means QEMU platform only supports GICV3, now it can support
> > both GICv2 and GICv3. The scope of support has been expanded
> > Not mean GICv3 is a legacy feature.
>
> You might be misleading a bit here.
> In the current configuration, Xen support GICv2, GICv3 and vgic.
> The only thing not supported is actually the new VGIC but this is an 
> unsupported feature not fully functional which shall be used with caution.
>
> What issue exactly do you have in Qemu configured for gicv2 when you use the 
> default configuration ?

I want to use NEW_VGIC with GICv2, but QEMU only select GICV3,  when
GICv3 is select, the NEW_VGIC can not be used.   I try the NEW_VGIC
with GICv2, not found issue. so I want to remove this limitation.
If  you think we should not support NEW_VGIC feature,  we can ignore
this patch.  thanks!

>
> Cheers
> Bertrand
>
> >
> >>
> >>>
> >>> Signed-off-by: Dongjiu Geng <gengdongjiu1@xxxxxxxxx>
> >>> ---
> >>>  xen/arch/arm/platforms/Kconfig | 10 +++++++++-
> >>>  1 file changed, 9 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/xen/arch/arm/platforms/Kconfig 
> >>> b/xen/arch/arm/platforms/Kconfig
> >>> index c93a6b2756..41e82a42ee 100644
> >>> --- a/xen/arch/arm/platforms/Kconfig
> >>> +++ b/xen/arch/arm/platforms/Kconfig
> >>> @@ -13,7 +13,15 @@ config ALL_PLAT
> >>>      automatically select any of the related drivers.
> >>>
> >>>  config QEMU
> >>> -     bool "QEMU aarch virt machine support"
> >>> +     bool "QEMU aarch virt machine support >= v3.1.0"
> >>
> >> This is a bit misleading. A user may select this thinking that this will
> >> select GICv3. However, this will not.
> >>
> >> This also raises the question of what is the default GIC version in QEMU
> >> (i.e. if you don't pass anything on the command line)? If this is GICv3,
> >> then I am afraid that this patch would be a no-go for me.
> >>
> >> Looking at overall discussion, you seem to push the patch only to allow
> >> building a tiny Xen for QEMU and the new vGIC.
> >>
> >> The default Xen (i.e. make defconfig) will also work on QEMU. Given that
> >> the new vGIC is a still in development, I am seriously considering to
> >> say that if you want to try it then you have to use the default
> >> configuration.
> >>
> >> @Dongjiu, is there any reason why you want to use the tiny QEMU config
> >> rather than the default configuration?
> >
> > Hi Julien, thanks for the reply, I do not use the tiny QEMU config. I
> > used the default configuration and selected the platform as QEMU.
> > But QEMU platform only slects GICV3, so I submit this patch to remove
> > the limitation because I want to use VGIC. VGIC can already support
> > GICv2 now.
> >
> >>
> >> @Bertrand, @Stefano, what do you think?
> >>
> >> Cheers,
> >>
> >> --
> >> Julien Grall
>