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

[Vikram Garhwal <vikram.garhwal@amd.com>]

Hi Julien,
On Tue, Aug 22, 2023 at 08:10:05PM +0100, Julien Grall wrote:
> 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@amd.com>
> > Acked-by: Henry Wang <Henry.Wang@arm.com>
> > Reviewed-by: Michal Orzel <michal.orzel@amd.com>
> > 
> > ---
> > 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?
Yes, that is correct. This series doesn't remove the nodes which are not added
by overlay before.

I will add a document file. Is this needs to be in .pandoc or .txt format?
> 
> Cheers,
> 
> -- 
> Julien Grall