Re: [RFC PATCH 0/5] Allow for removal of DT nodes and properties

[Rob Herring <robh@kernel.org>]

On Mon, Aug 28, 2023 at 04:09:29PM -0600, Simon Glass wrote:
> Hi Peter,
> 
> On Mon, 28 Aug 2023 at 14:29, Peter Robinson <pbrobinson@gmail.com> wrote:
> >
> > On Mon, Aug 28, 2023 at 6:54 PM Simon Glass <sjg@chromium.org> wrote:
> > >
> > > Hi Peter,
> > >
> > > On Mon, 28 Aug 2023 at 10:37, Peter Robinson <pbrobinson@gmail.com> wrote:
> > > >
> > > > On Mon, Aug 28, 2023 at 5:20 PM Simon Glass <sjg@chromium.org> wrote:
> > > > >
> > > > > Hi,
> > > > >
> > > > > On Sat, 26 Aug 2023 at 03:07, Sughosh Ganu <sughosh.ganu@linaro.org> wrote:
> > > > > >
> > > > > >
> > > > > > Provide a way for removing certain devicetree nodes and/or properties
> > > > > > from the devicetree. This is needed to purge certain nodes and
> > > > > > properties which may be relevant only in U-Boot. Such nodes and
> > > > > > properties are then removed from the devicetree before it is passed to
> > > > > > the kernel. This ensures that the devicetree passed to the OS does not
> > > > > > contain any non-compliant nodes and properties.
> > > > > >
> > > > > > The removal of the nodes and properties is being done through an
> > > > > > EVT_FT_FIXUP handler. I am not sure if the removal code needs to be
> > > > > > behind any Kconfig symbol.
> > > > > >
> > > > > > I have only build tested this on sandbox, and tested on qemu arm64
> > > > > > virt platform. This being a RFC, I have not put this through a CI run.
> > > > > >
> > > > > > Sughosh Ganu (5):
> > > > > >   dt: Provide a way to remove non-compliant nodes and properties
> > > > > >   fwu: Add the fwu-mdata node for removal from devicetree
> > > > > >   capsule: Add the capsule-key property for removal from devicetree
> > > > > >   bootefi: Call the EVT_FT_FIXUP event handler
> > > > > >   doc: Add a document for non-compliant DT node/property removal
> > > > > >
> > > > > >  cmd/bootefi.c                                 | 18 +++++
> > > > > >  .../devicetree/dt_non_compliant_purge.rst     | 64 ++++++++++++++++
> > > > > >  drivers/fwu-mdata/fwu-mdata-uclass.c          |  5 ++
> > > > > >  include/dt-structs.h                          | 11 +++
> > > > > >  lib/Makefile                                  |  1 +
> > > > > >  lib/dt_purge.c                                | 73 +++++++++++++++++++
> > > > > >  lib/efi_loader/efi_capsule.c                  |  7 ++
> > > > > >  7 files changed, 179 insertions(+)
> > > > > >  create mode 100644 doc/develop/devicetree/dt_non_compliant_purge.rst
> > > > > >  create mode 100644 lib/dt_purge.c
> > > > >
> > > > > What is the point of removing them? Instead, we should make sure that
> > > > > we upstream the bindings and encourage SoC vendors to sync them. If we
> > > > > remove them, no one will bother and U-Boot just becomes a dumping
> > > > > ground.
> > > >
> > > > Well things like the binman entries in DT are U-Boot specific and not
> > > > useful for HW related descriptions or for Linux or another OS being
> > > > able to deal with HW so arguably we're already a dumping ground to
> > > > some degree for not defining hardware.
> > >
> > > I have started the process to upstream the binman bindings.
> >
> > I don't think they should be in DT at all, they don't describe
> > anything to do with hardware, or generally even the runtime of a
> > device, they don't even describe the boot/runtime state of the
> > firmware, they describe build time, so I don't see what that has to do
> > with device tree? Can you explain that? To me those sorts of things
> > should live in a build time style config file.

For the record, I tend to agree.

> I beg to differ. Devicetree is more than just hardware and always has
> been. See, for example the /chosen and /options nodes.

There are exceptions...

> We need run-time configuration here, since we cannot know at build
> time what we will be asked to do by a previous firmware phase.

Really, I don't want to have to care about the binman binding. If it is 
u-boot specific, then it should stay in u-boot. I took /options/u-boot/, 
but now I'm starting to have second thoughts on that being in dtschema 
if it is going to be continually and frequently extended. Validating it 
in SR does little. If a vendor is abusing /options/u-boot/ in some way 
they could just as easily remove the node in their u-boot fork to pass. 
SR is certainly not going to require the node be there.

On A/B updates, that really doesn't seem like a u-boot specific problem 
to me. No one wants A/B updates in EDK2 or anything else?

Rob