From:   Alexander Stein <alexander.stein@ew.tq-group.com>
To:     Tim Harvey <tharvey@gateworks.com>
Cc:     Rob Herring <robh+dt@kernel.org>, Shawn Guo <shawnguo@kernel.org>,
        Sascha Hauer <s.hauer@pengutronix.de>,
        Pengutronix Kernel Team <kernel@pengutronix.de>,
        Fabio Estevam <festevam@gmail.com>,
        NXP Linux Team <linux-imx@nxp.com>,
        Device Tree Mailing List <devicetree@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>,
        Linux ARM Mailing List <linux-arm-kernel@lists.infradead.org>
Subject: Re: (EXT) Re: [PATCH] arm64: dts: imx8mm-venice-gw73xx-0x: add dt overlays for serial modes
Date:   Tue, 11 Jan 2022 08:20:01 +0100
Message-ID: <2226437.ElGaqSPkdT@steina-w>
Organization: TQ-Systems GmbH
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Am Dienstag, 11. Januar 2022, 01:00:21 CET schrieb Tim Harvey:
> [SNIP]
> > diff --git a/arch/arm64/boot/dts/freescale/Makefile
> > b/arch/arm64/boot/dts/freescale/Makefile index a14a6173b765..5ec8d59347b6
> > 100644
> > --- a/arch/arm64/boot/dts/freescale/Makefile
> > +++ b/arch/arm64/boot/dts/freescale/Makefile
> > @@ -44,6 +44,9 @@ dtb-$(CONFIG_ARCH_MXC) += imx8mm-var-som-symphony.dtb
> > 
> >  dtb-$(CONFIG_ARCH_MXC) += imx8mm-venice-gw71xx-0x.dtb
> >  dtb-$(CONFIG_ARCH_MXC) += imx8mm-venice-gw72xx-0x.dtb
> >  dtb-$(CONFIG_ARCH_MXC) += imx8mm-venice-gw73xx-0x.dtb
> > 
> > +dtb-$(CONFIG_ARCH_MXC) += imx8mm-venice-gw73xx-0x-rs232-rts.dtbo
> > +dtb-$(CONFIG_ARCH_MXC) += imx8mm-venice-gw73xx-0x-rs422.dtbo
> > +dtb-$(CONFIG_ARCH_MXC) += imx8mm-venice-gw73xx-0x-rs485.dtbo
> > 
> >  dtb-$(CONFIG_ARCH_MXC) += imx8mm-venice-gw7901.dtb
> >  dtb-$(CONFIG_ARCH_MXC) += imx8mm-venice-gw7902.dtb
> >  dtb-$(CONFIG_ARCH_MXC) += imx8mn-beacon-kit.dtb
> > 
> [SNIP]
> I'm mostly interested to see if my approach to dt fragments here and
> the naming of the files makes sense to others.
> 
> This patch causes the kernel to build dtbo files for:
> arch/arm64/boot/dts/freescale/imx8mm-venice-gw73xx-0x-rs232-rts.dtbo
> arch/arm64/boot/dts/freescale/imx8mm-venice-gw73xx-0x-rs422.dtbo
> arch/arm64/boot/dts/freescale/imx8mm-venice-gw73xx-0x-rs485.dtbo
> 
> The intention is that these files are used by boot firmware (U-Boot)
> to adjust the dtb before passing it to the kernel.

Hi Tim,

do these dtbo actually work? I'm wondering because I was trying to useoverlays 
myself and noticed that the had to be compiled with -@ for u-boot to be able 
to apply them. Apparently there are 2 possibilities:
* Set "DTC_FLAGS_[dtb] := -@" yourself
See https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/
commit/?id=e426d63e752bdbe7d5ba2d872319dde9ab844a07

* Use dedicated overlay target
See https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/
commit/?id=15d16d6dadf6947ac7f9a686c615995c5a426ce2

You use neither of them. IIRC just naming the target file .dtbo will not apply 
symbols (-Q) during dtc call. Can you verify using 'V=1'
Also I'm wondering which way is the best to go.

Best regards,
Alexander