Re: [PATCH 0/2] arm64: dts: qcom: apq8016-sbc-d3-camera: Convert to DT overlay

[Bryan O'Donoghue]

On 22/09/2023 21:58, Stephan Gerhold wrote:
> On Fri, Sep 22, 2023 at 09:47:07PM +0100, Bryan O'Donoghue wrote:
> > On 22/09/2023 16:11, Stephan Gerhold wrote:
> > > Follow the example of the recently added apq8016-sbc-usb-host.dtso and
> > > convert apq8016-sbc-d3-camera-mezzanine.dts to a DT overlay that can be
> > > applied on top of the apq8016-sbc.dtb. This makes it more clear that
> > > this is not a special type of DB410c but just an addon board that can
> > > be added on top.
> > >
> > > I also prepended a patch that cleans up the node names a bit.
> > >
> > > Signed-off-by: Stephan Gerhold <stephan@xxxxxxxxxxx>
> > > ---
> > > Stephan Gerhold (2):
> > >         arm64: dts: qcom: apq8016-sbc-d3-camera: Use more generic node names
> > >         arm64: dts: qcom: apq8016-sbc-d3-camera: Convert to DT overlay
> > >
> > >    arch/arm64/boot/dts/qcom/Makefile                    |  5 +++--
> > >    ...nine.dts => apq8016-sbc-d3-camera-mezzanine.dtso} | 20 ++++++++++++++------
> > >    2 files changed, 17 insertions(+), 8 deletions(-)
> > > ---
> > > base-commit: 7236e86ce5c8198b01c30933c2334d07d877cf48
> > > change-id: 20230922-apq8016-sbc-camera-dtso-f247bea40f99
> > >
> > > Best regards,
> >
> > db410c doesn't ship with a bootloader that is capable of applying a dtbo
> > though, so this conversion mandates an updated or chainloaded bootloader or
> > out-of-tree kernel patch to support.
> >
> > __adding__ is fine but, converting implies imposes a new requirement on the
> > bootchain.
> >
> > Perhaps a middle road solution is to
> >
> > - Add, not convert a standalone dtbo or
> > - Add a dtbo that includes the mezzanine dts but amends it
> >
> > Option 2 for preference but, I'm not sure the dts syntax can be meaningfully
> > made to do that.
>
> With these patches the apq8016-sbc-d3-camera-mezzanine.dtb is still
> magically built, by running fdtoverlay on apq8016-sbc.dtb and applying
> the dtbo. It's applied during the build process so you don't need a
> bootloader that supports DTBOs.
>
> There is literally *no change* for you in terms of usage. :-)

Ah I see

+apq8016-sbc-d3-camera-mezzanine-dtbs	:= apq8016-sbc.dtb 
apq8016-sbc-d3-camera-mezzanine.dtbo

I guess I like the idea of having the base board dtb a mezzanine.dtb and 
a dtbo that could be applied as an overlay to the base board dtb, 
optionally.

Our model then for mezzanine enablement wouild be

1. baseboard.dtb
2. baseboard-mezzanine.dtb
3. baseboard-mezzanine.dtbo

With booting #2 or #1+#3 resulting in the same image but, potentially 
allowing for

1. baseboard.dtb
2. baseboard-mezzanine.dtb
3. baseboard-mezzanine.dtbo
4. baseboard-some-other-mezzanine.dtb
5. baseboard-some-other-mezzanine.dtbo

#1 + #3 + #5 which would represent a hypothetical stacking of mezzanine 
boards.

As a model, I think that has merit.

Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@xxxxxxxxxx>