Re: [XEN][PATCH v9 05/19] xen/arm: Add CONFIG_OVERLAY_DTB

[Julien Grall <julien@xxxxxxx>]

Hi Vikram,

On 19/08/2023 01:28, Vikram Garhwal wrote:
> Introduce a config option where the user can enable support for adding/removing
> device tree nodes using a device tree binary overlay.
>
> Update SUPPORT.md and CHANGELOG.md to state the Device Tree Overlays support for
> Arm.
>
> Signed-off-by: Vikram Garhwal <vikram.garhwal@xxxxxxx>
> Acked-by: Henry Wang <Henry.Wang@xxxxxxx>
> Reviewed-by: Michal Orzel <michal.orzel@xxxxxxx>
>
> ---
> Changes from v7:
>      Add this feature as "experimental support" in CHANGELOG.md
> ---
> ---
>   CHANGELOG.md         | 3 ++-
>   SUPPORT.md           | 6 ++++++
>   xen/arch/arm/Kconfig | 5 +++++
>   3 files changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/CHANGELOG.md b/CHANGELOG.md
> index 7d7e0590f8..47098dbfca 100644
> --- a/CHANGELOG.md
> +++ b/CHANGELOG.md
> @@ -24,7 +24,8 @@ The format is based on [Keep a 
> Changelog](https://keepachangelog.com/en/1.0.0/)
>    - xl/libxl can customize SMBIOS strings for HVM guests.
>    - Add support for AVX512-FP16 on x86.
>    - On Arm, Xen supports guests running SVE/SVE2 instructions. (Tech Preview)
> -
> + - On Arm, experimental support for dynamic addition/removal of Xen device tree
> +   nodes using a device tree overlay binary(.dtbo).
Typo: missing space before (.

>   
>   ## [4.17.0](https://xenbits.xen.org/gitweb/?p=xen.git;a=shortlog;h=RELEASE-4.17.0) - 2022-12-12
>   
> diff --git a/SUPPORT.md b/SUPPORT.md
> index 35a6249e03..8eb006565c 100644
> --- a/SUPPORT.md
> +++ b/SUPPORT.md
> @@ -844,6 +844,12 @@ No support for QEMU backends in a 16K or 64K domain.
>   
>       Status: Supported
>   
> +### Device Tree Overlays
> +
> +Add/Remove device tree nodes using a device tree overlay binary(.dtbo).
Same here. I don't suggest to handle it on commit because this is not 
something I want to merge without the rest of the series.
> +
> +    Status, ARM: Experimental
> +
>   ### ARM: Guest ACPI support
>   
>       Status: Supported
> diff --git a/xen/arch/arm/Kconfig b/xen/arch/arm/Kconfig
> index fd57a82dd2..02c4796438 100644
> --- a/xen/arch/arm/Kconfig
> +++ b/xen/arch/arm/Kconfig
> @@ -92,6 +92,11 @@ config HAS_ITS
>           bool "GICv3 ITS MSI controller support (UNSUPPORTED)" if UNSUPPORTED
>           depends on GICV3 && !NEW_VGIC && !ARM_32
>   
> +config OVERLAY_DTB
> +       bool "DTB overlay support (UNSUPPORTED)" if UNSUPPORTED
> +       help
> +         Dynamic addition/removal of Xen device tree nodes using a dtbo.
Do we have any documentation in the tree of the limitations and how this 
works?
The reason I am asking is the wording here suggests that it would be 
possible to remove nodes from the original Device-Tree. AFAIU this is 
not possible with the implementation and you are not planning to handle 
it. Correct?
Cheers,

--
Julien Grall