linux-kernel - Re: [PATCH v2 2/6] arm64: dts: qcom: qcs6490-rb3gen2: Add DP output

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Message-ID: <CAA8EJpp1VBm5-x4W-yGrt+zq9keHWxTrucgsHCYqfLp-Fib1qg@mail.gmail.com>
Date: Fri, 29 Mar 2024 03:44:39 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Bjorn Andersson <quic_bjorande@...cinc.com>
Cc: Bjorn Andersson <andersson@...nel.org>, cros-qcom-dts-watchers@...omium.org, 
	Konrad Dybcio <konrad.dybcio@...aro.org>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley <conor+dt@...nel.org>, 
	Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, linux-arm-msm@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 2/6] arm64: dts: qcom: qcs6490-rb3gen2: Add DP output

On Fri, 29 Mar 2024 at 03:37, Bjorn Andersson <quic_bjorande@...cinc.com> wrote:
>
> On Thu, Mar 28, 2024 at 09:17:45AM +0200, Dmitry Baryshkov wrote:
> > On Thu, 28 Mar 2024 at 05:07, Bjorn Andersson <andersson@...nel.org> wrote:
> > >
> > > On Thu, Mar 28, 2024 at 03:51:54AM +0200, Dmitry Baryshkov wrote:
> > > > On Wed, 27 Mar 2024 at 04:04, Bjorn Andersson <quic_bjorande@...cinc.com> wrote:
> > > > >
> > > > > The RB3Gen2 board comes with a mini DP connector, describe this, enable
> > > > > MDSS, DP controller and the PHY that drives this.
> > > > >
> > > > > Signed-off-by: Bjorn Andersson <quic_bjorande@...cinc.com>
> > > > > ---
> > > > >  arch/arm64/boot/dts/qcom/qcs6490-rb3gen2.dts | 40 ++++++++++++++++++++++++++++
> > > > >  1 file changed, 40 insertions(+)
> > > > >
> > > > > diff --git a/arch/arm64/boot/dts/qcom/qcs6490-rb3gen2.dts b/arch/arm64/boot/dts/qcom/qcs6490-rb3gen2.dts
> > > > > index 63ebe0774f1d..f90bf3518e98 100644
> > > > > --- a/arch/arm64/boot/dts/qcom/qcs6490-rb3gen2.dts
> > > > > +++ b/arch/arm64/boot/dts/qcom/qcs6490-rb3gen2.dts
> > > > > @@ -39,6 +39,20 @@ chosen {
> > > > >                 stdout-path = "serial0:115200n8";
> > > > >         };
> > > > >
> > > > > +       dp-connector {
> > > > > +               compatible = "dp-connector";
> > > > > +               label = "DP";
> > > > > +               type = "mini";
> > > > > +
> > > > > +               hpd-gpios = <&tlmm 60 GPIO_ACTIVE_HIGH>;
> > > >
> > > > Is it the standard hpd gpio? If so, is there any reason for using it
> > > > through dp-connector rather than as a native HPD signal?
> > > >
> > >
> > > I added it because you asked for it. That said, I do like having it
> > > clearly defined in the devicetree.
> >
> > I asked for the dp-connector device, not for the HPD function change.
> >
>
> I didn't realize that you could have a dp-connector device without
> defining the hpd-gpios, but it looks like you're right.
>
> Do we have any reason for using the internal HPD, when we're already
> spending the memory to allocate the dp-connector device?

No, no particular reason. I was trying to understand if there was any
reason for that from your side.

Then:

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>

> PS. It's recommended that you dynamically switch to GPIO-based HPD in
> lower-power scenarios, as this allow you to turn off the DP controller
> and still detect plug events...

I don't think rb3g2 is a low-power device, but I think this is still a
valid argument.

-- 
With best wishes
Dmitry