Re: [RFC PATCH] arm/gicv2: make GICv2 driver and vGICv2 optional

[Julien Grall <julien@xxxxxxx>]

Hi,

On 02/08/2023 14:53, Luca Fancellu wrote:
> Introduce Kconfig GICV2 to be able to compile the GICv2 driver only
> when needed, the option is active by default.
>
> Introduce Kconfig VGICV2 that depends on GICV2 or GICV3 and compiles
> the GICv2 emulation for guests, it is required only when using GICV2
> driver, otherwise using GICV3 it is optional and can be deselected
> if the user doesn't want to offer the vGICv2 interface to guests or
> maybe its GICv3 hardware can't offer the GICv2 compatible mode.
>
> Signed-off-by: Luca Fancellu <luca.fancellu@xxxxxxx>
> ---
>   xen/arch/arm/Kconfig        | 13 +++++++++++++
>   xen/arch/arm/Makefile       |  4 ++--
>   xen/arch/arm/domain_build.c |  4 ++++
>   xen/arch/arm/gic-v3.c       |  4 ++++
>   xen/arch/arm/vgic.c         |  2 ++
>   5 files changed, 25 insertions(+), 2 deletions(-)
>
> diff --git a/xen/arch/arm/Kconfig b/xen/arch/arm/Kconfig
> index fd57a82dd284..dc702f08ace7 100644
> --- a/xen/arch/arm/Kconfig
> +++ b/xen/arch/arm/Kconfig
> @@ -78,6 +78,14 @@ config ARM_EFI
>           UEFI firmware. A UEFI stub is provided to allow Xen to
>           be booted as an EFI application.
>   
> +config GICV2
> +       bool "GICv2 driver"
> +       default y
> +       select VGICV2
> +       help
> +         Driver for the ARM Generic Interrupt Controller v2.
> +         If unsure, say Y
> +
>   config GICV3
>         bool "GICv3 driver"
>         depends on !NEW_VGIC
> @@ -92,6 +100,11 @@ config HAS_ITS
>           bool "GICv3 ITS MSI controller support (UNSUPPORTED)" if UNSUPPORTED
>           depends on GICV3 && !NEW_VGIC && !ARM_32
>   
> +config VGICV2
> +       bool "vGICv2 interface for guests"
This description is a bit misleading as the vGICv2 will also be used for 
dom0 in the case of vGICv2.
> +       default y
Please add a longer help.

> +       depends on (GICV2 || GICV3) && !NEW_VGIC
In the near future, I don't expect anyone to introduce a new non-GIC of 
interrupt controller for Arm. But I would expect new version of the GIC. 
So I would drop (GICV2 || GICV3).
Also when !NEW_VGIC is selected, this will make VGICV2 will be 
unselected. I was actually expecting the other way around given that new 
vGIC only offer v2 support.
The rest of the changes LGTM.

Cheers,

--
Julien Grall