Re: [PATCH] arm64: dts: qcom: Split sdm845-db845c to add headless support

[Amit Pundir]

On Mon, 5 Jun 2023 at 16:07, Krzysztof Kozlowski
<krzysztof.kozlowski@xxxxxxxxxx> wrote:
>
> On 05/06/2023 11:47, Amit Pundir wrote:
> > This is a follow-up of the upstream discussion,
> > https://lore.kernel.org/linux-kernel/20230124182857.1524912-1-amit.pundir@xxxxxxxxxx/T/#u,
> > around adding a reserved memory region in sdm845-db845c
> > for the framebuffer memory (the splash region set up by
> > the bootloader) but the general opinion was to avoid
> > adding that reserved memory for the headless DB845c
> > usecase.
> >
> > So this patch splits the sdm845-db845c into a common dtsi,
> > a new sdm845-db845-headless DT, which disables the mdss
> > display subsystem, and a new sdm845-db845c DT with an
> > additional reserved-memory region for the framebuffer.
> >
> > The default sdm845-db845c.dtb remains pretty much the same
> > (with an exception of additional reserved-memory region),
> > while others can use sdm845-db845c-headless.dtb for their
> > headless systems.
>
> You should describe the hardware in commit msg. What is "headless"? If
> no HDMI plugged in, then it is a NAK because plug or unplugged HDMI
> cable is not a property of a DTS.

Hi, my only intended goal [1] is to add a reserved-memory region
(specific to the framebuffer memory reserved by the bootloader for the
boot splash) in sdm45-db845c. But I have been told that reserving
these 30+ MBs for every DB845c is a waste in case we are not using
display at all (a headless system?). So I prepared this patch for RFC.
The definition of headless is ambiguous to me as well. It could be no
HDMI plugged in or no display drivers enabled at all. I believe it all
comes down to specific use cases.

As far as my use-case (vanilla AOSP) is concerned, display is a
critical component and device doesn't boot to completion unless it is
hooked to any kind of display. May I suggest we go back to my original
change [1] of adding a reserved-memory region for now and let the
users of a headless system, define or come up with their respective
use-case?

Regards,
Amit Pundir
[1] https://lore.kernel.org/linux-kernel/20230124182857.1524912-1-amit.pundir@xxxxxxxxxx/T/#u

>
> >
> > Signed-off-by: Amit Pundir <amit.pundir@xxxxxxxxxx>
> > ---
> > Please pick this after the lvs regulator nodes reordering patch
> > https://lore.kernel.org/lkml/20230602161246.1855448-1-amit.pundir@xxxxxxxxxx/T/#u.
> > I'll rebase and resend this patch otherwise.
> >
> >  arch/arm64/boot/dts/qcom/Makefile             |    1 +
> >  .../boot/dts/qcom/sdm845-db845c-common.dtsi   | 1178 +++++++++++++++++
> >  .../boot/dts/qcom/sdm845-db845c-headless.dts  |    9 +
> >  arch/arm64/boot/dts/qcom/sdm845-db845c.dts    | 1172 +---------------
>
> A lot of duplication. Are you sure you generated the patches with
> correct -M/-C/-B arguments to rename or copy?
>
> >  4 files changed, 1194 insertions(+), 1166 deletions(-)
> >  create mode 100644 arch/arm64/boot/dts/qcom/sdm845-db845c-common.dtsi
> >  create mode 100644 arch/arm64/boot/dts/qcom/sdm845-db845c-headless.dts
> >
> > diff --git a/arch/arm64/boot/dts/qcom/Makefile b/arch/arm64/boot/dts/qcom/Makefile
> > index 4f9e81253e18..22876ea2e409 100644
> > --- a/arch/arm64/boot/dts/qcom/Makefile
> > +++ b/arch/arm64/boot/dts/qcom/Makefile
> > @@ -166,6 +166,7 @@ dtb-$(CONFIG_ARCH_QCOM)   += sdm845-cheza-r1.dtb
> >  dtb-$(CONFIG_ARCH_QCOM)      += sdm845-cheza-r2.dtb
> >  dtb-$(CONFIG_ARCH_QCOM)      += sdm845-cheza-r3.dtb
> >  dtb-$(CONFIG_ARCH_QCOM)      += sdm845-db845c.dtb
> > +dtb-$(CONFIG_ARCH_QCOM)      += sdm845-db845c-headless.dtb
> >  dtb-$(CONFIG_ARCH_QCOM)      += sdm845-db845c-navigation-mezzanine.dtb
> >  dtb-$(CONFIG_ARCH_QCOM)      += sdm845-lg-judyln.dtb
> >  dtb-$(CONFIG_ARCH_QCOM)      += sdm845-lg-judyp.dtb
> > diff --git a/arch/arm64/boot/dts/qcom/sdm845-db845c-common.dtsi b/arch/arm64/boot/dts/qcom/sdm845-db845c-common.dtsi
> > new file mode 100644
> > index 000000000000..ecc4a851e29c
> > --- /dev/null
> > +++ b/arch/arm64/boot/dts/qcom/sdm845-db845c-common.dtsi
> > @@ -0,0 +1,1178 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright (c) 2019, Linaro Ltd.
> > + */
> > +
> > +/dts-v1/;
> > +
> > +#include <dt-bindings/leds/common.h>
> > +#include <dt-bindings/pinctrl/qcom,pmic-gpio.h>
> > +#include <dt-bindings/regulator/qcom,rpmh-regulator.h>
> > +#include <dt-bindings/sound/qcom,q6afe.h>
> > +#include <dt-bindings/sound/qcom,q6asm.h>
> > +#include "sdm845.dtsi"
> > +#include "sdm845-wcd9340.dtsi"
> > +#include "pm8998.dtsi"
> > +#include "pmi8998.dtsi"
> > +
> > +/ {
> > +     model = "Thundercomm Dragonboard 845c";
> > +     compatible = "thundercomm,db845c", "qcom,sdm845";
>
> So it is the same hardware? Why compatible is in common part? I don't
> understand this change.
>
> Best regards,
> Krzysztof
>