Re: [PATCH v5 06/26] arm: qemu: Add a devicetree file for qemu_arm64

[Tom Rini]

On Tue, Nov 02, 2021 at 07:32:54PM -0600, Simon Glass wrote:
> Hi Tom,
> 
> On Tue, 2 Nov 2021 at 10:57, Tom Rini <trini@konsulko.com> wrote:
> >
> > On Tue, Nov 02, 2021 at 08:59:45AM -0600, Simon Glass wrote:
> > > Hi François,
> > >
> > > On Mon, 1 Nov 2021 at 11:33, François Ozog <francois.ozog@linaro.org> 
> > > wrote:
> > > >
> > > > Hi Simon
> > > >
> > > > Le lun. 1 nov. 2021 à 17:58, Simon Glass <sjg@chromium.org> a écrit :
> > > >>
> > > >> Hi Peter,
> > > >>
> > > >> On Mon, 1 Nov 2021 at 04:48, Peter Maydell <peter.maydell@linaro.org> 
> > > >> wrote:
> > > >> >
> > > >> > On Tue, 26 Oct 2021 at 01:33, Simon Glass <sjg@chromium.org> wrote:
> > > >> > >
> > > >> > > Add this file, generated from qemu, so there is a reference 
> > > >> > > devicetree
> > > >> > > in the U-Boot tree.
> > > >> > >
> > > >> > > Signed-off-by: Simon Glass <sjg@chromium.org>
> > > >> >
> > > >> > Note that the dtb you get from QEMU is only guaranteed to work if:
> > > >> >  1) you run it on the exact same QEMU version you generated it with
> > > >> >  2) you pass QEMU the exact same command line arguments you used
> > > >> >     when you generated it
> > > >>
> > > >> Yes, I certainly understand that. In general this is not safe, but in
> > > >> practice it works well enough for development and CI.
> > > >
> > > > You recognize that you hijack a product directory with development hack 
> > > > facility. There is a test directory to keep things clear. There can be 
> > > > a dev-dts or something similar for Dev time tools.
> > > > I have only seen push back on those fake dts files in the dts 
> > > > directory: I guess that unless someone strongly favors a continuation 
> > > > of the discussion, you may consider re-shaping the proposal to address 
> > > > concerns.
> > >
> > > As stated previously, I would like to have at least a sample DT
> > > in-tree for all boards. I cannot see another way to get the Kconfig
> >
> > What's the point of having a sample when it's not going to always be
> > correct or may be actively wrong and we can tell interested developers /
> > users how to get the correct DTB/DTS to examine?
> >
> > > options in line. If we are able to put these files somewhere else in
> > > the future and get them out of U-Boot, with perhaps just an overlay
> > > for development purposes, I'd be keen to see it. But for now, this is
> > > where we are, I believe.
> > >
> > > In this particular case, this is not just a dev hack. It is also for
> > > CI tests which need to use a devicetree. See for example here:
> > >
> > > https://patchwork.ozlabs.org/project/uboot/patch/20211101011734.1614781-15-sjg@chromium.org/
> > > https://patchwork.ozlabs.org/project/uboot/patch/20211101011734.1614781-24-sjg@chromium.org/
> >
> > This example would probably be better done on vexpress_ca9x4 where we do
> > test in CI via QEMU but do not need to modify a device tree that is
> > passed on to us, we already control the source of truth DTB in this
> > case.
> 
> But that board:
> 
> - uses OF_EMBED, which it should not
> - does not use SPL, which I need

Check out the other hardware then that we emulate today, and or maybe
something off of
https://qemu.readthedocs.io/en/latest/system/target-arm.html that we
could add.  My point is that by picking the QEMU targets for where to
test this feature you've gone with "I've introduced this feature so now
I need to introduce this other change I've been arguing for too" in an
artificial manner as it would only be used like that for testing.

-- 
Tom

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