linux-kernel - Re: [PATCH 09/21] arm64: dts: qcom: sc8280xp: Add PCIe bridge node

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Date: Sun, 17 Mar 2024 22:37:15 -0500
From: Bjorn Andersson <andersson@...nel.org>
To: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc: Konrad Dybcio <konrad.dybcio@...aro.org>, 
	Rob Herring <robh+dt@...nel.org>, Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, 
	Conor Dooley <conor+dt@...nel.org>, cros-qcom-dts-watchers@...omium.org, 
	linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 09/21] arm64: dts: qcom: sc8280xp: Add PCIe bridge node

On Thu, Feb 22, 2024 at 11:09:58AM +0530, Manivannan Sadhasivam wrote:
> On Wed, Feb 21, 2024 at 01:39:01PM +0100, Konrad Dybcio wrote:
> > On 21.02.2024 04:41, Manivannan Sadhasivam wrote:
> > > On Qcom SoCs, the PCIe host bridge is connected to a single PCIe bridge
> > > for each controller instance. Hence, add a node to represent the bridge.
> > > 
> > > While at it, let's remove the bridge properties from board dts as they are
> > > now redundant.
> > > 
> > > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> > > ---
> > >  .../dts/qcom/sc8280xp-lenovo-thinkpad-x13s.dts     |  8 -----
> > >  arch/arm64/boot/dts/qcom/sc8280xp.dtsi             | 40 ++++++++++++++++++++++
> > >  2 files changed, 40 insertions(+), 8 deletions(-)
> > > 
> > > diff --git a/arch/arm64/boot/dts/qcom/sc8280xp-lenovo-thinkpad-x13s.dts b/arch/arm64/boot/dts/qcom/sc8280xp-lenovo-thinkpad-x13s.dts
> > > index def3976bd5bb..f0a0115e08fa 100644
> > > --- a/arch/arm64/boot/dts/qcom/sc8280xp-lenovo-thinkpad-x13s.dts
> > > +++ b/arch/arm64/boot/dts/qcom/sc8280xp-lenovo-thinkpad-x13s.dts
> > > @@ -733,14 +733,6 @@ &pcie4 {
> > >  	status = "okay";
> > >  
> > >  	pcie@0 {
> > > -		device_type = "pci";
> > > -		reg = <0x0 0x0 0x0 0x0 0x0>;
> > > -		#address-cells = <3>;
> > > -		#size-cells = <2>;
> > > -		ranges;
> > > -
> > > -		bus-range = <0x01 0xff>;
> > > -
> > >  		wifi@0 {
> > 
> > This doesn't seem right, pleas use a label
> > 
> 
> Why? A node label is useful if we want to reference it at the root level in
> board dts, but here it is not.
> 

Giving the bridge a label and then adding wifi@0 as a child using that
label in the dts is pretty much how we do for everything else.

I find this over-flattening hard to follow, but relying on child node
names when extending the structure or adding properties have bitten us
many times in the past.

As such, I think the desired result in the dts should be:

&pcie4 {
	status = "okay";
};

&pcie4_bridge {
	wifi@0 {
		...
	};
};

Regards,
Bjorn

> - Mani
> 
> -- 
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