[PATCH 1/4] fdt: add support for adding pmem nodes

[Simon Glass]

Hi Sughosh,

On Mon, 28 Oct 2024 at 12:29, Sughosh Ganu <sughosh.ganu at linaro.org> wrote:
>
> On Sun, 27 Oct 2024 at 20:30, Simon Glass <sjg at chromium.org> wrote:
> >
> > Hi Sughosh,
> >
> > On Fri, 25 Oct 2024 at 13:15, Sughosh Ganu <sughosh.ganu at linaro.org>
wrote:
> > >
> > > From: Masahisa Kojima <kojima.masahisa at socionext.com>
> > >
> > > One of the problems OS installers face, when running in EFI, is that
> > > the mounted ISO after calling ExitBootServices goes away. For some
> > > distros this is a problem since they rely on finding some core
packages
> > > before continuing the installation. Distros have works around this --
> > > e.g Fedora has a special kernel command line parameter called
> > > inst.stage2 [0].
> > >
> > > ACPI has NFIT and NVDIMM support to provide ramdisks to the OS, but we
> > > don't have anything in place for DTs. Linux and device trees have
support
> > > for persistent memory devices. So add a function that can inject a
pmem
> > > node in a DT, so we can use it when launhing OS installers with EFI.
> > >
> > > [0]
> > >
https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/7/html/installation_guide/chap-anaconda-boot-options#sect-boot-options-installer
> > >
> > > Signed-off-by: Masahisa Kojima <kojima.masahisa at socionext.com>
> > > Signed-off-by: Sughosh Ganu <sughosh.ganu at linaro.org>
> > > ---
> > >  boot/fdt_support.c    | 41 +++++++++++++++++++++++++++++++++++++++--
> > >  include/fdt_support.h | 13 +++++++++++++
> > >  2 files changed, 52 insertions(+), 2 deletions(-)
> >
> > Can you please use the ofnode interface for this? We are trying not to
> > add more of this kind of fixup, as it means someone will have to port
> > it over later.
> >
> > See EVT_FT_FIXUP
>
> Are you suggesting using the EVT_FT_FIXUP interface for adding the
> pmem node? If so, how does this work on platforms which enable
> livetree? Looking at the code, I see that the EVT_FT_FIXUP gets called
> only when the livetree is not active. However, I am not able to find
> any place where the livetree is getting disabled. We do have a
> function, oftree_to_fdt() which flattens a livetree, but I don't see
> it getting called from anywhere except from a 'upl' command. The
> of_root pointer does get set in initr_of_live(), but apart from
> dm_test_pre_run(), I do not see where we disable the livetree and set
> of_root to NULL.
>
> So on platforms which do enable livetree, how does this fixup work?
> What am I missing?

It isn't implemented yet for OF_LIVE in image_setup_libfdt(). Most of the
code is there though. It just needs to be hooked up - see oftree_to_fdt()
and oftree_from_fdt().

The idea would be to remove the of_live_active() check, so the event is
always sent (will need to 'select EVENT' for OF_LIVE).

Then in that same code, after the event, call oftree_to_fdt() and copy the
fdt back to blob.

If you have time, it should be a nice mini project and will allow us to
migrate more things to the ofnode API.

Regards,
Simon